
Class 

Book 

Copyriglit}^^. 



COPYRIGHT DEPOSIT. 



GENERAL INORGANIC 
CHEMISTRY 



BY 



CHARLES BASKERVILLE, Ph.D., 

PROFESSOR OF CHEMISTRY IN THE COLLEGE 
OF THE CITY OF NEW YORK 



BOSTON, MASS. 
D. C. HEATH & CO., PUBLISHERS 

1909 






Copyright, 1908, 
By D. C. Heath & Co. 



LIBRARY of CONGRESS 
Two CoDies Received 
JUL ^ I ittW« 

l2- / 7jji 



PREFACE 

The value of a text-book depends upon its teachableness. 
The teachableness of a book or method, however, depends 
also upon the teacher, his spirit and the conscientious 
interpretation of the serious but opportune responsibility 
that he enjoys. What is contained within these pages has 
been tried with a large number of students in general 
chemistry through several years. Satisfactory results have 
been obtained. That is why it is now offered to others. 

The author has unhesitatingly used every source of 
information, and all devices suggested by other teachers 
which appealed to him, to make the work effective. The 
material has been so arranged as to accomplish the most 
in the least time. Much has been omitted, and the temp- 
tation to omit more has been resisted with difficulty. 

A knowledge of elementary physics has been assumed, 
but where the border territory of chemical physics has 
been entered, sufficient of the general principles involved 
has been recapitulated, but without detail, to present a 
logical sequence. No effort has been made to get away 
from the conception of atoms, yet enough of the modern 
theories of physical chemistry has been presented to show 
the student the entrancing fields of interest to the special- 
ist and the scientific methods he makes use of therein. 
A distinct effort has been made to keep theory and fact in 
proper proportion, yet some very definite statements are 
made; but it is assumed that the teacher will expkin that 
some of the laws are true only within limits. 

Many historical errors handed down through genera- 
tions of texts have been corrected. Many methods of 
preparation used by the alchemist and given in texts these 
days have been omitted. As a rule, only methods which 
illustrate principles have been given. 



iv PREFACE 

Illustrations and lecture experiments, with a. few excep- 
tions, have been omitted, for the teacher then has latitude 
in presenting the subject. Every laboratory is provided 
with some apparatus and a lantern, or perhaps a projecto- 
scope, which is to be had now at a small cost; and each 
teacher has devised lecture experiments, or has used 
Benedict's or Newth's Lecture Experiments, or other works. 

Students should take notes on the experiments, write 
them up at home, and submit them with answers to the 
questions and problems which are appended to each chap- 
ter. The two latter do not always deal with the facts and 
principles developed in that particular chapter. This 
causes the student to keep in mind a constant review of 
what has been studied and impresses the application of 
the principles. Reference and conversion tables, so con- 
venient in the back of a book, are purposely omitted. A 
copy of Biedermann's Cheinikej^-Kalender, or Olsen's An- 
nual, should be available in each laboratory. The student 
thus learns how to look up necessary data. Knowledge 
gained by extra labor sticks. 

A Laboratory Manual by the author and Dr. Robert W. 
Curtis, of the same department, is used in conjunction with 
the text. In it further emphasis is placed upon the obser- 
vation and correlation of facts and the applications of the 
underlying principles. It is our practice during the latter 
part of the work to assign chapters for parallel reading in 
Venable's Short History of Chemistry. 

Drs. Curtis, Estabrooke, and Prager, and Messrs. Breit- 
hut and Whitaker, of this department, have been helpfully 
suggestive, but thanks are especially due to my private 
assistant, Mr. W. A. Hamor, who has followed the proof 
closely and has prepared the index. 

CHARLES BASKERVILLE. 

College of the City of New York, 
May I, 1909. 



CONTENTS 

CHAPTER PAGE 

I. Introduction i 

II. The ChexMical Elements . . . . . .15 

III. Hydrogen . . . ,. 22 

IV. Oxygen — Ozone . 29 

V. Water ^4 

VI. Water — Practical Considerations . , . 39 

VII. Water — Theoretical Considerations ... 44 

VIII. The Halogens 51 

IX. Halogen Acids 60 

X. The Alkali Metals . . . , . . .66 

XI. Nitrogen — Ammonia — Liquefaction of Gases — 

Compound Radicals 72 

XII. The Air and its Constituents — The Noble Gases - 78 

XIII. Carbon 86 

XIV. Carbon Hydrides — Flame — Illuminants . . 91 
XV. Carbon Oxides — Valence 97 

XVI. The Periodic Law 104 

XVII. Group VI. Negative Series: Oxygen, Sulphur, 

Selenium, Tellurium 113 

XVIII. Group V. Negative Series: Nitrogen, Phos- 
phorus, Arsenic, Antimony, Bismuth . . .118 
XIX. Group II. Positive Series : Alkaline Earth Ele- 
ments 125 

XX. Group III. The Earth Elements— The Rare 

Earth Elements . . . . . . .129 

XXI. Group IV. Carbon-Silicon Group. . . . 136 

V 



VI 



CONTENTS 



CHAPTER 

XXII. 



XXIII. 

XXIV. 

XXV. 

XXVI. 

XXVII. 

XXVIII. 

XXIX. 



XXX. 

XXXI. 
XXXII. 
XXXIII. 

XXXIV. 

XXXV. 
XXXVI. 

XXXVII. 

XXXVIII. 
XXXIX. 

XL. 

XLI. 
XLII. 
XLIII. 



Group II. Negative Series: Zinc, Cadmium, 
Mercury 

Group I, Negative Series: Copper, Silver, 
Gold 

Positive Series of Groups V, VI, VII 

Radium and Radio-active Phenomena 

Group VIII. The Iron Metals 

The Platinum Metals 

Hydrogen Compounds of the Elements 

Halogen Compounds of the Elements, or 
Halides — Groups I, II, and III ; Photo-chem- 
istry 

Halogen Compounds of the Elements, or 
Halides — Groups IV, V, VI, VII, and VIII . 

Determination of Molecular Weights . 

Theory of Electrolytic Dissociation 

Oxides, Sulphides, Hydroxides, Hydrosul- 
phides 

Oxides, Hydroxides, Sulphides, and Hydro- 
sulphides OF Group I 

Oxides and Sulphides of Group II . 

The Oxides and Sulphides of Group III 

Oxides and Sulphides of Group IV. Car- 
bonates OF Group I 

Carbonates of the Remaining Groups 

Silicon Oxides, Silicates, Glass, Earthenware 

The Remaining Oxides and Sulphides of 
Group IV 

Nitrogen Oxides and their Derivatives 

Nitric Acid and the Nitrates . . . . 

Oxides and Sulphides of the Other Ele- 
ments OF Group V 



144 

149 

157 
163 
169 
178 
183 



191 

199 
205 
211 

216 

221 
229 

235 

241 
247 

252 

259 
263 
268 

274 



CONTENTS 



Vll 



CHAPTER 

XLIV. The Oxides and Hydroxides of Sulphur . 

XLV. The Sulphates — Alums 

XLVI. Other Oxides of Group VI and their Deriva- 
tives 

XLVII. Oxides of the Negative Members of Group VII 

XLVIII. Oxides and Sulphides of Manganese . 

XLIX. Oxides and Sulphides of Group VIII . 

L. Binary Compounds of Groups IV and V 

LI. Compounds of Carbon and Nitrogen . 

LII. Alloys 



PAGE 
282 

290 



296 

315 
321 

325 
331 



GENERAL INORGANIC CHEMISTRY 



CHAPTER I 
INTRODUCTION 

The study of the phenomena of nature and the specu- 
lations arising from the facts observed, looking to an 
orderly and systematic arrangement of the knowledge 
obtained, is called science. It inquires for the sake of 
knowledge alone. The application of this knowledge for 
production, protection, or any utilitarian purpose what- 
ever, constitutes an art, hence we have pure and applied 
scie?ice. The practical applications of science have often 
been of great service in the advancement of our knowledge 
of pure science, therefore no antagonism should exist, as 
the two branches are mutually helpful. 

Nature is so vast and comprehensive a subject, that it 
has become necessary, with our increasing knowledge of 
its complexities, to divide its study into several branches. 
For example, when we study bodies as they are presented to 
us, at rest or in motion, we call the s\ih]QCt physics. When, 
however, changes occur in the composition of those bodies, 
through any agency whatever, we call it chemistry. In 
inanimate nature rocks crumble to dust through physical 
and chemical changes, and we have geology. Reaching 
into space gives us astronomy, the physics and chemistry 
of celestial bodies. When life forces become involved, 
we have biology, and so on. This is more or less an artifi- 
cial and arbitrary, but a distinctly convenient, subdivision. 



2 GENERAL INORGANIC CHEMISTRY 

Even these branches are subdivided. Chemistry may be 
descriptive, analytical, physiological, and so forth. 

Chemistry may be defined as the study of matter and 
the changes produced in it by the action of chemical 
force, or other forms of energy, upon it. As it is primarily 
an experimental science, we may begin its study by means 
of experiments. 

Experiment I. If we heat a platinum wire in the air, we 
observe that it gets red-, or even white-hot. On removing 
it from the flame it cools, and we have the wire in its origi- 
nal form. We may heat it sufficiently hot to melt it, or 
even convert it into a vapor, but we have made no change 
in the platinum. It is the same material with which we 
started, although we may have changed it into the three 
physical states — solid, liquid, and gas. These are physical 
changes.* If we weigh the platinum before and after 
heating, we find it has neither gained nor lost in weight. 

Experiment II. If we heat a magnesium wire in the 
air, we observe that it burns with a -brilliant light and is 
converted into a white powder, in no way resembling the 
original material. An actual change in the physical prop- 
erties of the metal has occurred. In this instance it has 
been initiated by heat and has continued with the produc- 

* From his knowledge of physics, the reader is supposed to know what is 
understood by such terms as matter, molecule, physical states, fusion, melting- 
point (m.-p. ), evaporation, b o Hi 7ig- point (b.-p.), distillation, distillate, subli- 
viation, calories, late7it and specific heat, specific gravity, the laws of the con- 
servation of matter arid energy. 

If the assumption is unwarranted, the reader should at once review his 
physics and postpone the study of chemistry until he has acquired a proper 
foundation, for we must of necessity describe the materials w^hich enter into 
chemical transformations and the products obtained by their physical attri- 
butes. 



INTRODUCTION 3 

tion of heat and light. If we weigh the white powder, we 
find its weight is greater than that of the original mag- 
nesium wire. By this chemical change the magnesium 
has added something to itself, which must have come from 
the air. • The powder weighs two thirds more ; that is, the 
ratio between the magnesium wire (whatever amount is 
taken) and the white powder is 3 : 5. 

Experiment III. If we place some red oxide of mer- 
cury in a hard-glass test-tube and heat it, we observe a 
change of color. As the heat increases, and as long as it 
is applied or until all the red material disappears from the 
bottom of the tube, we note a vapor given off which con- 
denses as a brilliant metallic mirror on the cooler walls of 
the tube. If we invert the tube over a piece of paper and 
tap it, we collect lustrous globules of quicksilver, very 
different from the red powder we heated. If, before heat- 
ing, we had lighted a splinter of wood, blown out the flame 
after a good red coal had formed, and inserted it into the 
tube before heating, we should have observed that the- coal 
gradually ceased to glow, as it does in the air. In other 
words, ordinary air was above the powder in the tube. If 
this is repeated after the heating has begun and when the 
mirror is forming, the glowing coal bursts into a flame. If 
we cease heating the tube, the formation of the mirror 
ceases. This shows the necessity for the continued appli- 
cation of heat. If we again insert a glowing splinter into 
the tube after all the red powder has disappeared from the 
bottom of the tube, we note that it no longer bursts into 
flame. The vapor of quicksilver, therefore, cannot be the 
substance which makes the splinter burn. If we weigh 
the tube and red oxide at the beginning and at the end of 
the experiment, we learn that something has been driven 
off. A gas was evidently given off, something like air. 



4 GENERAL INORGANIC CHEMISTRY 

being invisiblej yet different from the air, as shown by the 
conduct of the spHnter. The loss in weight is exactly -^^ 
of the red body. 

Experiment IV. If we place a hard lump of quick- 
lime, a cubic centimeter in size, in a tube and pour 2 cc. of 
water upon it, we observe that the lump swells up, crum- 
bles down into a fine powder, the water seems to disappear, 
and the tube gets hot. The characteristic properties of 
the quicklime and water have given way in their combina- 
tion. Energy in the form of heat has become evident in 
the change. 

Experiment V. If we examine some brimstone (sul- 
phur), we note among other things that it is yellow and 
not attracted by a magnet, but it seems to disappear in a 
liquid called carbon disulphide ; that is, it dissolves.* If 
we examine some iron filings, among other things we 
observe their metallic appearance. They are attracted by 
a magnet and are insoluble in carbon disulphide. 

If we mix 7 g. of these fihngs and 4 g. of sulphur inti- 
mately by grinding in a mortar, and apply a magnet to a 
portion of the mixture, the iron is drawn away and the 
sulphur remains behind. Or, if we put another part of 
the mixture in a bottle, pour in some carbon disulphide, 
and shake, the sulphur goes into solution. This may be 
shown by pouring off the liquid and allowing it to evapo- 
rate, when we find the yellow crystals of the sulphur in 
the vessel into which the liquid was poured. The iron re- 
mains behind. We can, in fact, make a perfect separation 
of the sulphur from the iron by repeatedly washing the iron 

* When a substance seems to disappear in a liquid in this manner, we 
have a solution. The substance dissolved is called the solute. The liquid 
used to make the solution is the solvent. If, on evaporation of the solvent, 
we recover the unchanged solute, we call it a simple solution. 



INTRODUCTION 5 

with fresh carbon disulphide. The characteristic physical 
properties, the individualities of the iron and sulphur, have 
remained the same. In fact, we are able, using a good 
magnifying glass, to pick the particles of iron and sulphur 
out of the mixture with a needle. 

if, however, we place a third portion in a test-tube and 
heat it a few minutes, we observe that a part begins to 
glow. The glow proceeds throughout the mass, even after 
we cease heating it. If we allow the mass to cool, we note 
that it has become black and does not resemble either the 
iron or sulphur. We are unable to pick particles of either 
out with a needle when we examine it with the magnifying 
glass. The mass is uniform in appearance. It is not at- 
tracted by the magnet. Carbon disulphide does not dis- 
solve it. The individualities of the iron and sulphur have 
apparently been lost. A new body, with characteristic 
properties of its own, has been produced, inaugurated 
through the agency of heat, but once begun, it proceeds 
until completed. 

Experiment VI. If we evaporate 100 cc. of water con- 
taining an acid, as hydrochloric acid, we obtain no residue. 
If we place a piece of zinc in a similar solution, we note 
that the metal dissolves. A gas is given off, which need 
not concern us at present. If we evaporate the solution 
obtained, we get a white residue which does not resemble 
the zinc in the least. By tests, of which we shall learn 
later, the presence of the zinc may be shown. It has not 
been lost.* 

Experiment VII. If we connect two sheets, one of 
zinc and the other of platinum, about 10 cm. square, to the 
terminals of a galvanometer and dip them into a beaker 

* When the individuality of the solute is changed in this manner, we call 
it a chemical solution. 



6 GENERAL INORGANIC CHEMISTRY 

containing an acid, we get indications of an electric cur- 
rent. A chemical change occurs. The zinc disappears, 
but is not lost, for if we evaporate the solution, we get a 
residue similar to that referred to in the last paragraph. 

Experiment VIII. If we insert two sheets of platinum, 
about 10 cm. square, into a water solution of copper sul- 
phate, and connect them with the terminals of an electric 
battery, we observe the formation of a red metallic deposit 
on one of the terminals and the gradual disappearance of 
the blue color of the liquid. 

From these observed facts we learn : — 

Firsts actual changes in the individuaHty of a substance 
may take place, differing from the physical changes. 
These we call chemical changes. This constitutes our first 
conclusion. 

Second, chemical changes may take place with or among 
any of the three physical states of matter, soHd (red oxide), 
liquid (quicksilver), or gaseous (oxygen gas, which made 
the glowing splinter burst into flame). 

Third, chemical changes may be merely inaugurated or 
continued by the influence of one of the forms of physical 
energy, heat or electricity, for example. 

Fourth, chemical changes may proceed without the 
initial or continuous aid of one of the varieties of physical 
energy, yet these changes appear to be accompanied by 
evidences of such energy. Therefore, we arrive at a sec- 
ond conclusion ; namely, chemical changes are intimately 
associated with, or attributable to, another form of energy, 
which we may call chemical energy or chemical affinity. 
At one time it was called chemism. 

Joule demonstrated the laiu of the conservation of energy. 
If the physical forms of energy, like heat, light, and so 
forth, are convertible into chemical energy, and vice versa, 



INTRODUCTION 7 

we assume that this constitutes no exception, although 
frankly we are not able to prove it absolutely. No case of 
chemical action has ever been observed, and many thou- 
sand careful studies have been made, without evidences 
of other forms of energy. Chemical actions are always 
accompanied by heat demonstrations (either absorption or 
evolution),* often by electricity as well, and frequently by 
light, and even sound. On account of this contamination, 
as it were, we do not at present know any accurate method 
of measuring this chemical affinity. 

Experiment IX. If we shake i g. of sodium chloride 
(table salt) crystals in 50 cc. of water, a clear solution is 
obtained. If we boil off the water, we get back our crys- 
tals of salt. If this is done carefully, we lose none of the 
salt, and apparently there has been no change in that sub- 
stance. If we dissolve 3 g. of silver nitrate in 50 cc. of 
water, we get another simple solution. If we pour the two 
clear solutions together, a white clotty solid is formed at 
once. This may be separated by filtering.! 

If the filtrate is evaporated and carefully dried, a white 

* When heat is given out, the action is exothermic. When heat is absorbed, 
endother?nic. As a rule, the tendency is in the direction of the evolution of 
heat. 

t When we produce a solid, that is, a substance which is insoluble in the 
liquid present, by bringing two clear solutions together, we call it a precipi- 
tate. The substance added to produce the precipitation is the precipitant. 
We may separate the precipitate from the liquid by filtering. The process 
oi filtration depends upon passing the liquid, in which the precipitate is 
suspended, through a porous material which is itself usually not affected by 
the liquid or solid and which should have pores so small that the solid is held 
back, yet the liquid passes freely. The liquid, after it has been filtered, is 
called the. filtrate. Sometimes the solid passes through also, and the filtrate 
is turbid. This indicates that tlie pores are too large or that the precipitate 
has not been sufficiently agglomerated. To accomplish this requires special 
treatment, which varies with substances and conditions. Filters are made of 
unsized paper, cloth, sand, glass-wool, asbestos, and so forth. 



8 GENERAL INORGANIC CHEMISTRY 

crystalline substance is obtained, which we find weighs 
about 1.5 g. If we moisten a piece of paper with a water 
solution of this body, dry it, and set it afire, it burns vigor- 
ously with a yellow flame. If we do the same with a solu- 
tion of the original sodium chloride, the paper burns with 
a yellow flame, but very slowly. If we do the same with 
a solution of the silver nitrate, the paper burns vigorously, 
but no yellow flame is obtained. It is reasonable to sup- 
pose that there is something in common with the salt and 
the residue which produced the yellow flame. It is also 
reasonable to think that there is something in common 
with the silver nitrate and the residue which causes the 
paper to burn in a lively manner. 

The clotty precipitate, being insoluble* in water, is quite 
different from the other two substances, and has been pro- 
duced by their presence in the same liquid. If it is col- 
lected by filtration, washed, and dried, we find it weighs 
about 2.5 g. 

Tho. fifth fact observed is that the sum of the weights of 
the new substances produced by the action (precipitate plus 
residue from evaporated filtrate in this case) is equal to the 
sum of the weights of the two materials used originally 
(salt and silver nitrate). Therefore (third conclusion), 
chemical energy which produces deep-seated changes in mat- 
ter^ neither creates nor destroys it. Chemical energy there- 
fore presents no evidence in opposition to the law of the 
conservation of matter. Lavoisier, in 1783, demonstrated 
this when he performed the third experiment, weighing the 
red oxide, quicksilver, and oxygen. 

If we perform Experiment V. by heating a mixture of 
8 g. of iron and 4 g. of sulphur instead of 7 and 4 g. respec- 

* As all substances are more or less soluble in water, when we use the term 
insoluble, we actually mean extremely slightly soluble. 



INTRODUCTION " 9 

lively, we observe some iron is removable from the 
ground-up mass by the magnet, but not all. No sulphur 
is removed by carbon disulphide. If a mixture of 7 g. of 
iron and 5 g. of sulphur is treated similarly, no magnetic 
properties are noted, but a portion of the sulphur, although 
not all, is removed by carbon disulphide. We must have 
the iron and sulphur in the exact proportion of 7 \ 4 in 
making the new body, to avoid having some iron or sul- 
phur left over. 

Any excess of either substance involved in a chemical 
change remains as such unused ; this constitutes a sivt/i 
fact from which we may draw a fourth conclusion ; namely, 
every substance has a definite composition. A definite 
amount of one substance requires a fixed ratio of a second 
substance to produce a third. 

The union of substances is called synthesis, and the prod- 
uct obtained a compound {Y.yi^. IL). A definite amount of 
one substance breaks up into a fixed ratio of two or more 
other substances (Exp. III.). . This rupture of a compound is 
spoken of as analysis. When we have exhausted all means 
at our command for breaking a substance up into other C9n- 
stituents, we say it is a simple substance. Compounds are 
composed of simple substances and always in definite fixed 
proportions, which facts give us the law of consta7icy of 
composition or definite proportions. We know of no excep- 
tions to this law, and we know the composition of many 
tens of thousands of compounds. 

Experiment X. If we take two glass cylinders, each of 
I 1. capacity, provided with ground tops and glass covers, 
we may fill them with gases. A description of the pro- 
cedure is unnecessary, as practice in the manipulation is 
had in the laboratory. We fill one cylinder with the gas 
obtained from aqua ammonia. We fill the other with a 



10 GENERAL INORGANIC CHEMISTRY 

gas obtained from muriatic acid. We note that bothi are 
colorless, fume in the air, and each has its own distinct 
sharp odor. By applying a little vaseline to the glass 
covers, the gases may be safely confined within the cylin- 
ders. One cylinder is inverted and placed upon the other, 
so that the glass covers form a partition separating the two 
gases. By a deft movement this partition may be with- 
drawn, the mouths of the cylinders fitting snugly, and the 
gases are brought together. At once a dense white cloud 
forms, but this soon settles as a white powder upon the 
walls and bottom of the cylinders. A chemical change has 
taken place. A solid has been produced when the initial 
substances were gases. 

Because gases expand and contract through wide ranges 
of volume under the influence of changing pressures and 
temperatures, we say they are in molecular condition. 
Chemical changes take place between molecules is our fifth 
conclusion. 

This must also be true for those changes which occur 
in solutions. Our reason for making this statement de- 
pends upon a few simple facts. If we remove equal 
amounts from the top, middle, and bottom of a salt solu- 
tion, like the one used above (Exp. IX.), we find them 
equally salty and on analysis that they have the same 
composition. If the same amount of salt is dissolved in 
twice, or any number of times, that volume of water, we 
find the solid uniformly distributed throughout the hquid. 
In other words, the salt in solution is distributed through- 
out the volume of the liquid, whatever volume it may 
occupy. Gases distribute themselves throughout the vol- 
ume of the containing vessel as molecules, therefore it 
appears that the solid (or other form of substance) in solu- 
tion is in a similar condition. Demonstrations of chemical 



INTRODUCTION 1 1 

affinity are facilitated by those conditions zvhich give mole- 
cules the greatest freedom of motion. 

Experiment XL If we repeat Experiment III., using 
the greenish black oxide instead of the red oxide of quick- 
silver, we observe first a mirror and at the same time the 
production of the red form, but no oxygen gas is generated. 
On continuing the heat, this red form gives the same 
results as that used in the former experiment ; hence it is 
the same material. If we weigh the tubes in both in- 
stances at the beginning and end of the experiments, we 
note that the ratio of quicksilver in the red oxide to the 
gas given off is 25 : 2 and with the other oxide 50 : 2. 

We see that two different compounds may break up into 
the same two simple substances, but in different propor- 
tions ; or the converse, two simple substances may combine 
in different proportions to form two different compounds. 
In this case we observe just twice as much quicksilver in 
one substance as in the other, that is, a multiple. From 
examination of many thousands of compounds, it has been 
learned that this is always the case ; hence we have our 
sixth conclusion, namely, the law of multiple proportions, 
that is to say, there must be some minimum amount of 
each simple substance which enters every compound, either 
as such or some multiple. 

When we endeavor to understand the facts observed 
and the conclusions drawn, a tentative explanation is first 
put forward. This is an hypothesis. When accumulated 
facts accord with the hypothesis, it is termed a theory. 

From the facts obtained from the experiments, we are 
warranted in reaching the same conclusion arrived at by 
John Dalton in 1803, although he used different experi- 
ments ; namely, that chemical action takes place between 
molecules, and. that the molecules are composed of smaller, 



12 GENERAL INORGANIC CHEMISTRY 

invisible, indivisible, unchangeable particles which he called 
atoms. An atom is the minimum amount of a simple sub- 
stance. As matter has weight, — that is, upon our globe 
it is attracted through the agency of gravity, — the molecules 
of which matter is composed must have weight. In turn, 
if the molecules are composed of atoms, the latter must 
have weight; this we call the atomic zvcight. As many 
thousands of facts observed during the last century have 
been in accord with this hypothesis, it has become known 
as the atomic theory and has been of inestimable value in 
the development of our knowledge of the science of 
chemistry. 

Within the last decade of the nineteenth century, how- 
ever, experimental evidence has been obtained, which, ac- 
cording to one school of scientific men, has thrown some 
doubt on the theory as generally accepted. This in brief 
is as follows. The hydrogen molecule, the lightest known 
molecule, has been supposed to be made of hydrogen 
atoms, the lightest atoms known. Thirty years ago 
Crookes found that an electric current could be passed 
with great ease through hydrogen gas under extremely 
small pressures. He suggested the existence of an ultra- 
gaseous state of matter, a protyle, of which all matter is 
composed, and that its particle weighs about one thousandth 
that of a hydrogen atom. J. J. Thomson, following an 
elaborate procedure, weighed these particles, not singly, of 
course, but in quantity, and found that the value was 
between 800 and 1000. As they bear electric charges, 
he designated them electi'ons (corpicscles, according to 
Lodge). 

By definition, an atom means something which can- 
not be divided. We have been accustomed to apply 
the term to that chemical particle which has not yet 



INTRODUCTION " 13 

been divided. As soon as it is shown to be complex, the 
particle ceases to be an atom. As language changes, there 
can be little objection, if it be done by common agree- 
ment, so there may be no misunderstanding, to applying 
the term electron to a real atom or the real indivisible 
particle. Men of science do not hesitate to discard one 
theory to accept a better one, yet they do not embrace 
the new simply on account of its novelty. The evidence 
accumulated at present is scarcely sufficient to warrant 
the abandonment of the atomic theory, especially when it 
is used so satisfactorily for the purpose of systematizing 
chemical science. 

EXERCISES * 

1. How does a simple solution differ from a chemical solution ? 

2. What are the grounds for assuming that substances in the 
gaseous state are in the molecular condition ? 

3. Suppose two solutions, when brought together, produce a 
solid. How may we collect this solid, and what principles are in- 
volved in that collection ? 

4. Is the line of argument outlined in this chapter leading to 
the assumption of the existence of atoms logical ? If so, why so ? 
If not, why not ? And what other conclusion would you draw, and 
why ? 

It is the everlasting duty of science to seek the truth, as 
far as we are able to conceive it. If the conclusions are 

* The reader is advised to give the closest attention to these exercises. It 
is urged that he write out a solution of each problem presented. A clear ex- 
position will show his understanding of the facts to which attention is directed 
and the principles involved. Some exercises are given which, serve to refresh 
what has been previously treated. Students should be required every w^eek, 
as a part of the home work, to submit notebooks containing a full account, 
in their own words, of these exercises. If this is done conscientiously, ex- 
amination time will carry none of its usual bugbears. 



14 GENERAL INORGANIC CHEMISTRY 

not logical, it is not science. True, our logic, may appear 
false at times through our lack of knowledge or the misin- 
terpretation of facts. This latter we should avoid ; there- 
fore, the utmost frankness between teacher and student 
must prevail. 



CHAPTER II 
THE CHEMICAL ELEMENTS 

We know many different kinds of substances. As a 
molecule is the smallest particle of a substance which 
exhibits the individuality of the substance, there must be 
as many different kinds of molecules as there are different 
kinds of substances. However, we know only about eighty 
different kinds of atoms. These atoms, singly or combined 
in twos, threes, or in larger numbers, give us the great 
variety of substances known. In compound molecules 
there are two or more different kinds of atoms. In 
addition to those combinations which we find in nature, 
numerous other combinations have been brought about 
in the laboratory, and yearly many are added to the list. 
Perhaps the possible number of compounds might be 
determined mathematically, but such a calculation would 
be a tedious and prolonged labor. This impresses itself 
when we later learn that thirteen carbon and twenty-eight 
hydrogen atoms may combine, theoretically, in 802 dif- 
ferent ways, giving corresponding compounds. Even a 
consideration of all known substances would be an unin- 
teresting task; but a study 01 the systems which have 
been evolved and the principles underlying these systems 
is one of great fascination. 

This may best be begun by a consideration of the simple 
substances, those whose molecules contain only one kind 
of atom. These we call the elements. The elements may 
have only one atom in the molecule or several. It follov^s 

15 



l6 GENERAL INORGANIC CHEMISTRY 

that the number of elements must be Umited to the num- 
ber of different kinds of atoms known. We may discover 
some unknown at present or we may show the complexity 
of some now thought to be simple, but the actual number 
of different kinds of elements in the world cannot be 
added to nor taken from. 

In this connection it should be said that a philosophical 
idea has come forward at intervals ever since man began 
pondering on these matters ; namely, that there is, or was, 
one, the simplest substance of which all matter is, or was, 
made. If that be true, — and perhaps it is, — then we 
only require the knowledge of how to change one element 
into another and the necessary apparatus to make the idea 
an accomplished fact. The thought was prominent in the 
discussions Vv^ith and even before the early Greek philoso- 
phers. It dominated the pre-chemistry period, when the 
true alchemists, like Geber in the eighth century, and their 
charlatan camp followers, sought to change silver and the 
other metals into gold. It prevailed for a long time after 
Roger Bacon in the thirteenth century said that nature 
had made the change, but that it had taken ages to 
accomplish it. The true end, he said, should be the find- 
ing or making of the *' philosopher's stone," with a pinch 
of which man could accomplish those changes in a short 
period. With the final estabHshment of the law of the con- 
servation of matter by Lavoisier in the last quarter of the 
eighteenth century, the idea appeared to be doomed from 
an experimental point of view. Within the past decade 
a new element, radium (Chap. XXV), has been discovered. 
Under certain conditions, it changes into another element, 
hehum (Chap. XII). The transmutation of the elements has 
been experimentally demonstrated. While these statements 
appear to be contradictory, in fact they are not, when the 



THE CHEMICAL ELEMENTS 1 7 

terms used are clearly understood. By our definition, 
radium cannot be an element, because its molecule breaks 
up into something else, yet it has a recognized place in the 
table of elements. This latter fact is due to an agreement 
among chemists to recognize a substance as an element 
which, under proper conditions, exhibits a spectrum show- 
ing characteristic lines possessed by no other element and 
possesses a definite combining weight. Radium satisfies 
these two requirements and constitutes an exception to the 
general proposition of the consistency of atoms in an ele- 
mentary molecule. If we retain the term clement, and 
there is no indication of its being discarded soon, its defi- 
nition must be broadened. 

Of the several hundred substances which have been 
proposed as chemical elements, only about eighty have 
been agreed upon.* On the next page will be found an 
alphabetical list of the elements recognized at the present 
time (1909). Owing to the progress of science this is not 
fixed and unchangeable, new elements being added from 
time to time, others being removed when resolved into con- 
stituents. Oftentimes, when that occurs, the name of the 
complex is given to one of its constituents (lanthanum was 
broken up into lanthanum and didymium). No changes 
are made, however, without a most thorough scrutiny on 
the part of many. 

No general system has been followed in naming the 
elements. Some have been known from the earliest times, 
and their common names have persisted in use. In most 
cases such names have followed the linguistic changes 
(iron, copper). Some have been named after some char- 
acteristic property they possess (chlorine, bromine), or 

* A complete list of these, with full information, is to be found in " The 
Chemical Elements " by the author, from the press of John Wiley & Sons, 
New York. 



GENERAL INORGANIC CHEMISTRY 



THE CHEMICAL ELEMENTS 



INTERNATIONAL ATOMIC WEIGHTS, 



Aluminum 
Antimony } 
(Stibium*) ^ 
Argon . . . 
Arsenic . . 
Barium . . 
Beryllium } 
(Glucinum f ) ) 
Bismuth 
Boron . 
Bromine 
Cadmium 
Caesium 
Calcium 
Carbon 
Cerium . 
Chlorine 
Chromium 
Cobalt . 
Columbium } 
(Niobium f) ^ 
Copper (Cuprum 
Dysprosium , 
Erbium . , 
Europium . . 
Fluorine . , 
Gadolinium . 
Gallium . . 
Germanium . 
Gold (Aurum 
Helium . . 
Hydrogen 
Indium . , 
Iodine . . . 
Iridium . . 
Iron (Ferruni)* 
Krypton . , 
Lanthanum . 
Lead (Plumbum 
Lithium . . 
Lutecium . , , 
Magnesium 
Manganese 
Mercury 



(Hydrargyrum*) ^ 

* Alternate Latin names. 



Al 


27.1 


Sb 


120.2 


A 


39-9 


As 


75.0 


Ba 


i37 37 


Be 




^rGl 9-1 1 


Bi 


208.0 


B 


II.O 


Br 


79-92 


Cd 


112.40 


Cs 


132.81 


Ca 


40.09 


C 


12.00 


Ce 


140.25 


CI 


3546 


Cr 


52.1 


Co 


58.97 


Cb 




^rNb 935 | 


Cu 


63-57 


Dy 


162.5 


Er 


167.4 


Eu 


152.0 


F 


19.0 


Gd 


157-3 


Ga 


699 


Ge 


72.5 


Au 


197.2 


He 


4.0 


H 


1.008 


In 


1 14.8 


I 


126.92 


Ir 


193. 1 


Fe 


55-85 


Kr 


81.8 


La 


139.0 


Pb 


207.1 


Li 


7.00 


Lu 


174 


f/ 


24.32 


Mn 


54-93 


Hg 


2000 



Molybdenum 
Neodymium 
Neon . . 
Nickel . . 
Nitrogen 
Osmium . . 
Oxygen . . 
Palladium . 
Phosphorus 
Platinum 
Potassium } 
(KaHum*) (" 
Praseodymium 
Radium 
Rhodium 
Rubidium . 
Ruthenium . 
Samarium . 
Scandium . 
Selenium . 
Silicon . . 
Silver 

(Argentum *) 
Sodium 
(Natrium *) 
Strontium . 
Sulphur . , 
Tantalum . 
Tellurium . 
Terbium 
Thallium 
Thorium 
Thuhum 
Tin (Stannum *) 
Titanium . . 
Tungsten 
(Wolframium *) 
Uranium . . 
Vanadium . . 
Xenon . . . 
Ytterbium (neo-) 
Yttrium . . . 
Zinc .... 
Zirconium . . 



1909 

Mo 

Nd 

Ne 

Ni 

N 

Os 

O 

Pd 

P 

Pt 

K 

Pr 
Ra 
Rh 
Rb 
Ru 
Sa 
Sc 
Se 
Si 



Na 

Sr 

S 

Ta 

Te 

Tb 

Tl 

Th 

Tm 

Sn 

T 

W 

U 

V 

Xe 

Yb 

Yt 

Zn 

Zr 



96.0 

144-3 
20.0 
58.68 
14.01 

190.9 
16.00 

106.7 
31.0 

1950 

3910 

140.6 
2264 
102.9 

85.45 
101.7 
150,4 
44.1 
79.2 
28.3 

10788 

23 00 

87.62 
32.07 
181.0 
127.5 
159.2 
204.0 
232.42 
168.5 
1190 
48.1 

1840 

238-5 
51.2 

128 

172 
89.0 

65-37 
90.6 



t Alternate names. 



THE CHEMICAL ELEMENTS 19 

compound in which they occur (nitrogen), or the planets 
(uranium), or some mythological character (thorium, tan- 
talum), or the country of the discoverer (gallium, ger- 
manium). The names of many of the so-called metallic 
elements end in *'-ium." 

The accepted atomic weight is placed in the. third 
column. In other places we shall learn some of the 
principles underlying the determination of these figures, 
but one or two points require explanation here. The 
figures are not absolute, but relative. For instance, 1 1 
opposite boron does not mean 1 1 grams, 1 1 pounds, 1 1 
tons, or any definite weight except in comparison with the 
other elements. If we have 23 grams, pounds, or tons 
of a compound whose molecule contains one atom each 
of boron and carbon, we have present 11 grams, pounds, 
or tons of boron and 12 of carbon. 

As they are relative, we are at liberty to select any unit 
as a basis. It would be only natural to place the lightest 
at I ; and this was done for a while, but we find none in 
our table with that figure. We find for hydrogen 1.008. 
If hydrogen were placed at i, then the value for oxygen 
would be 15.89, whereas it appears as 16. The reason for 
this is purely utilitarian. The chemists of one nation used 
hydrogen i and oxygen 15.89, while chemists of another 
nation used hydrogen 1.008 and oxygen 16. There was no 
uniformity even among the chemists of any one nation. 
Consequently there was constant confusion in scientific 
literature and often grave differences in commercial trans- 
actions, due to the use of one value here and the other else- 
where. As the value is determined mainly from the com- 
pounds, and oxygen forms compounds with more of the 
different elements, especially the metals, than does hydro- 
gen, it was agreed among the majority of chemists, through 



20 



GENERAL INORGANIC CHEMISTRY 



accredited representatives, to regard oxygen as the standard 
and place its value at i6. No figure beyond the second 
decimal place is used for any element, except hydrogen, 
whose value in direct comparison with oxygen has been 
most accurately determined. 

In the middle column will be found the symbols of each 
element. They are used not only for abbreviation, as 
the figure ''7" is used instead of the word ''seven" 
in mathematical calculations, but often to indicate an 
atom or molecule, or a definite relative weight of the 
element. These symbols" are selected by taking the 
initial letter of the name, the Latin name being used 
where shown, and writing it as a capital. If there are sev- 
eral with the same initial letter, as carbon, cadmium, 
calcium, chlorine, cobalt, copper, etc., it is followed by a 
characteristic small letter in the name, in this manner: 
C, Cd, Ca, CI, Co, Cu, etc. It is not necessary to mem- 
orize these names, atomic weights, or symbols at once. 
Their frequent use soon makes one sufficiently familiar 
with them. 

Clarke has calculated the relative abundance of the 
elements in a sphere comprising the crust of the earth for 
a depth of ten miles, the ocean, and the atmosphere. 













PER CENT 1 


Oxygen 49.98 


Silicon . 










25 


30 


Aluminum . 










7 


26 


Iron . . . 










5 


08 


Calcium 










3 


51 


Magnesium 










2 


50 


Sodium 










2 


28 


Potassium . . 










2 


23 


Hydrogen . 













94 


Titanium . 













30 



PER CENT 

Carbon 0.21 

Clilorine 1 

^ . V 0.15 

Bromine ) 

Phosphorus 0.09 

Manganese 0.07 

Sulphur 0.04 

Barium 0.03 

Nitrogen 0.02 

Chromium o.oi 



THE CHEMICAL ELEMENTS 21 

There are several variable factors in the table, which 
prevent its being absolute. The composition of the 
interior of the earth is not known. All the elements are 
not included in the list, especially those with the largest 
atomic weights, hence, although interesting, we may select 
another method for inaugurating the study of the elements 
than one founded upon abundance. As the atomic weight 
is fixed, we may begin either with the Hghtest or the 
heaviest. Inasmuch as the lightest element is a con- 
stituent, with the most abundant one, in the most plentiful 
compound and familiar substance, water, we may begin 
with that. 

EXERCISE 

Draft a clear explanation of what is meant by a chemical 
element. 



CHAPTER III 
HYDROGEN 

The freezing of water, melting of ice, boiling of water, 
and condensation of steam illustrate the ease with which a 
familiar substance may be converted from one physical 
state into another. These changes are regarded by some 
as chemical, for ice, water, and steam exhibit distinct 
individualities. The molecules of ice, water, and steam, 
however, contain the same atoms and in the same propor- 
tions, so for our purposes we may regard them as the 
same.* We may ask them some chemical questions, as it 
were, by experiments. 

Experiment L If some iron filings are placed in a tube 
which is heated red hot, and we pass steam through the 
tube, we observe that iron rust has been formed; and the 
excess of steam coming from the exit, after condensation, 
shows the presence of a colorless gas not present as such 
in the original steam. This gas is not given off by the 
iron when heated alone, nor does it produce rust when 
passed over fresh iron. The iron rust weighs more than 
the original iron. This shows that a metal may take 
something away from the steam. The water molecule 

* We do not know the number of atoms in a molecule of water or ice, 
although we do for steam. This is a good illustration of the close relationship 
between the several branches of science and the difficulty in drawing a sharp 
line between physics and chemistry. 

22 



HYDROGEN '23 

must be made up of at least two kinds of atoms, one that 
causes iron to rust and one that does not. What are they? 

Experiment II. It is more convenient to experiment 
with Hquids, where possible, than with gases on account of 
the difficulties in handhng the latter. In this experiment 
we shall use water, and a different metal, as iron does not 
rust in pure water. If we place a piece of red litmus 
paper * in some water in a beaker or other suitable vessel, 
we note that it becomes wet. If we throw a piece of 
sodium on the water, we observe that it melts, spins 
around, and finally disappears. The water now not only 
wets the litmus paper but turns it blue. A chemical 
change has taken place. We know this without the litmus 
test, as the sodium melted, became a globule, and finally 
disappeared. Heat was produced, perhaps enough to heat 
the water next the bead of molten metal sufficiently to 
make a cushion of steam, which, escaping from under- 
neath, caused it to spin upon the surface of the water. 
But from the former experiment we suspect the produc- 
tion of a colorless gas. If now we repeat the experiment, 
using a pneumatic trough | and confining the sodium in a 
wire-gauze basket so that we may submerge the metal and 
conveniently collect any gas produced sufficiently insoluble 
in water to admit of its collection in that way, we do ob- 
tain a gas. It is colorless, like air ; it is also odorless, 
tasteless, and only slightly soluble in water, as shown by 
our ability to collect it over water (1000 volumes of water 

* Litmus is a purple coloring matter extracted from certain lichens. Un- 
sized, so-called filter or bibulous, paper is dipped into a water extract of lit- 
mus and allowed to dry. 

t The pneumatic trough is a vessel used for the collection of gases over 
a liquid, usually water. It seems to have been invented by Hales. As some 
gases are soluble in water, Priestley used mercury as the Uquid. 



24 GENERAL INORGANIC CHEMISTRY 

dissolve 19 volumes of the gas). However, if we remove 
the vessel in which the gas has been collected, having 
closed it with a sheet of glass, we may prove that it is not 
air by bringing it near a flame, when, on removing the 
cover, the gas takes fire and burns with a colorless flame. 
It may show a slightly yellow color, but that is due to the 
sodium present in the water. 

The substance formed in the water and which turns the 
litmus blue is known as caustic soda, .or sodium hydroxide. 
The chemical change, interaction, or reaction^ as it is 
usually termed, may be written as follows : — • 

Water + sodium —5^ hydrogen + sodium hydroxide, 
or, if we use the symbols : — 

HOH + Na->f H + NaOH. 
The horizontal arrow shows the direction in which the 
reaction proceeds. The vertical arrow pointing upwards 
indicates that it is a gas and escapes from the liquid. It 
will be observed that the sum of the atoms on one side of 
the horizontal arrow is equal to that on the other ; hence, 
this is more frequently written with the equality sign ( = )• 
Such an expression as *'NaOH," which indicates the 
presence of one atom each of sodium, oxygen, and hydro- 
gen in the sodium hydroxide, is called a chemical formula. 
When more than one atom of an element is present, it is 
indicated by a numeral subscript at the right. For ex- 
ample, the formula of water is H2O. In writing a 
formula, usually the metallic substance, or that which acts 
like one, is placed first. When the atoms of only two ele- 
ments are present in the compound, it is binary. In nam- 
ing the compound the name of the second element is 
modified so that it ends in '' -ide," and thus becomes de- 
scriptive; for example, a binary compound of oxygen is an 



HYDROGEN 25 

oxide ; of chlorine, a chloride ; and so forth. The whole re- 
action written with symbols is called a chemical eqitation. 
These equations are very important and are constantly 
used, but the impression that they constitute chemistry must 
be avoided. Yet they give us much information ; for exam- 
ple, the symbols tell the relative weights of the elements 
entering the reaction, and it will be noted that the sums of 
the atomic weights on each side of the equation are equal. 

H2O +Na=H+ NaOH. 

1x2 = 2-1-16 23-fi6-hi 

18 23 I -f 40 

41 41 

Long before the conduct of steam with hot iron was 
understood, or the conduct of water with sodium (Davy 
separated the metal for the first time just a century ago) 
was heard of, the existence of this gas was known. It 
was found when Paracelsus (1493-1541) obtained an in- 
flammable gas by the action of acids upon metals, but he 
did not prove that it was different from other inflammable 
gases. De Mayerne (1650) produced it from iron and sul- 
phuric acid. This method for producing it is one of the 
few very old procedures not outgrown in the progress of 
chemistry and is constantly in use to-day. Such a process 
we may illustrate in — 

Experiment .III. Zinc -h hydrogen chloride = hydro- 
gen and zinc chloride : 

Zn -F 2HClT±f H2 4-ZnCl2. 

In this equation we have another feature illustrated. 
When several molecules of one kind are involved in a re- 



26 GENERAL INORGANIC CHEMISTRY 

action, we indicate the number by a figure placed before 
the entire formula of the substance. For example, 2 HCi 
means that two hydrogen chloride molecules are necessary, 
and that not only two hydrogen but two chlorine atoms are 
present. We also note that hydrogen is combined with 
one chlorine atom, whereas zinc combines with two. 

The gas is the lightest substance known. Some volcanic 
gases contain it, but it diffuses more rapidly than any 
other gas, so it is found free in the air in extremely small 
amounts (less than i in 30,000). It is found in small 
cavities in a few rare minerals. The spectroscope shows 
its presence in the sun. It is 14.39 times lighter than air. 
It therefore has a specific gravity of 0.06949. One liter 
at 0° * and under 760 mm. pressure weighs 0.089 g-j equal 
to one crith. One gram of it will fill 11. 12 1. at zero and 
under normal pressure. It may be collected by upward 
displacement. It is a good conductor of heat, but a poor 
conductor of sound. By cooling to — 243°, it has been 
converted into a Hquid with a specific gravity of 0.07 at 
that temperature. At — 255° it becomes a white crystaUine 
solid (Dewar). These characteristics are designated as 
the pJiysical properties. 

It burns in the air with a non-luminous flame (philoso- 
pher's or Dobereiner's lamp), producing moisture (Macquer, 
1766). Cavendish and Watt (1781) also observed the pro- 
duction of water when the gas was burned in air. Lavoisier 
(1783) named it hydrogen, from vhdip r^evvdeiv (to pro- 
duce water). 

Hydrogen has a strong afifinity for what are called neg- 
ative elements. It combines with oxygen and chlorine, 
under proper conditions, with explosive violence and the 

*A11 temperatures in this book are centigrade (C.) unless stated otherwise. 



HYDROGEN 2/ 

generation of heat. More heat (68,000 calories) is pro- 
duced when hydrogen is burned in oxygen than in any 
chemical reaction known. It shows little tendency to com- 
bine with electro-positive (metallic) elements, yet it does 
form such compounds as LiH2, Na4H2, K4H2. Palladium 
can condense 980 times its volume of hydrogen, and the 
latent heat made sensible in this apparent change from the 
gaseous to the solid state is sufficient to cause it to combine 
with oxygen. Finely divided platinum will also do this. 
These characteristics are known as chemical properties. 

In the free condition it is not poisonous, but when 
breathed it weakens the voice and gives it a higher pitch. 

It occurs in all acids, is combined with oxygen in water, 
combined with carbon in natural gas and petroleum, and 
with carbon, oxygen, and other elements in all living matter. 

The production of so much heat during its combustion 
is utilized in the oxyhydrogen lamp for lead burning, the 
smelting of platinum, producing the lime-light, and so forth. 
Numerous technical processes for its production commer- 
cially, as heating carbon with slaked lime, and freezing the 
other gases out of producer gas by means of hquid air, have 
met with failure. An alloy of sodium with lead.(*'hy- 
drone"), when in contact with water, generates hydrogen 
most satisfactorily. 

If we place the terminals of a direct current of electric- 
ity in pure water, no evidence of a flow of electricity is 
observed. If the water has an acid, that is, a sour sub- 
stance, added to it, the current passes. This is shown not 
only by electrical instruments, but by the escape of gases 
at each terminal. If these gases are collected with suitable 
apparatus, we observe that both are colorless and odorless, 
but one has twice the volume of the other. On testing the 
one with the larger volume, we learn that it is hydrogen. 
The other we shall study in the next chapter. 



28 GENERAL INORGANIC CHEMISTRY 

EXERCISES 

1. Give the typical methods used in making hydrogen and 
emphasize the important features. 

2. Why may hydrogen be collected by upward displacement? 
What is meant by the diffusion of gases and what laws govern it? 

3. What do the following two equations tell from the principles 
already presented ? 

(i). Mg + 2HCl-±MgCl2 + i^H2; 
(2). Zn + 2 NaOH :± Na2Zn02 + f H2. 
(Refer to table, p. 18.) 



CHAPTER IV 
OXYGEN — OZONE 

Oxygen, O. At. Wt., i6. M. Wt, 32 

For several centuries it has been known that a portion 
of the air is fixed by certain metals when they are heated 
in it (Jean Rey, 1630). Some metals fix a part of the air 
on exposure to it, without evidence of measurable heat; 
for instance, iron rusts in the air. Mayow (1674) ob- 
tained a gas which he called *'nitro-aerial spirit," by heat- 
ing niter. Scheele (i 771-1777) prepared *' aer vitriolicus," 
** fire air," or "life air," by heating several oxygen com- 
pounds, among them black oxide of manganese. To 
Priestley (1774), however, is given the honor of discover- 
ing that part of the air which is fixed by metals. In accord 
with the nomenclature of the day, he called it " dephlogis- 
ticated air." He obtained it by heating mercuric oxide 
(Experiment III, Chapter I) with sunlight concentrated 
by a lens. Lavoisier (i 774-1 781) explained its relation to 
oxidation, combustion, and respiration. Considering it 
an ** acidifying principle," or constituent of all acids, he 
named it oxyghie from o^v^ ^evvdeiv (to produce acid). 

It occurs (I) free and (II) combined. 

I. It constitutes one fifth by volume and one fourth by 
weight of the air. 

II. {a) As oxides : water, H.2O ; silica, Si02 ; iron 
oxide, Fe203 ; carbon dioxide, CO2. 

{h) In compounds with two or more other elements, 
called salts : limestone (calcium carbonate), CaCOg ; heavy 

29 



30 GENERAL INORGANIC CHEMISTRY 

spar (barium sulphate), BaS04 ; mica (potassium alumi- 
num orthosilicate), KAlSiO^. 

(c) It is a component of most animal and vegetable 
matter, as urea (CONgH^) Vnd sugar (C12H22O11). 

It is the most abundant of all the elements, forming 
about one half of all the matter of the earth's surface. 

Oxygen is prepared by a number of different ways. 
Five different methods are given, as each one illustrates a 
principle. 

Firsts by heating certain oxides, as 

2 HgO 1;: 2 Hg 4- O2 (above + 300°), 
and 
BaOg ~^ BaO + O (above + 1000° ; reforms at + 500°). 
Second, by the electrolysis of water : — 
2 H2O :;t 2 H2 + O2. 

Third, by heating certain salts which contain a large 
proportion of oxygen, as potassium chlorate: 

2 KCIO3 :± 2 KCH- f 3 O2. 

This reaction takes place best at + 350°, but with 
greater smoothness and at a lower temperature (+200°) 
when some manganese dioxide is added. 

Fourth, from liquid air. 

Fifth, very conveniently, by treating sodium dioxide 
(" oxone ") with" water : 

2 Na202 -f 2 H2O -± 4 NaOH + f O2. 

Physical Propei^ties. It is a colorless, odorless, tasteless 
gas, with a specific gravity of 1.1056 and a density of 15.89. 
One liter at zero and 760 mm. pressure weighs 1.429 g. 
One hundred volumes of water dissolve 4 volumes at zero 



OXYGEN 31 

atid 3 volumes at + 15°. One hundred volumes of absolute 
alcohol dissolve 28 volumes of oxygen. It boils at — 184°. 
The liquid, which is of a bright blue color, has a specific 
gravity of 1.124 at — 184°. Its critical temperature is 
— 118° and critical pressure 50 atmospheres. 
• Chemical Properties. It is non-combustible, but is a 
powerful supporter of combustion. The combustion usu- 
ally occurs with the production of much heat and often 
light. Oxygen compounds are known of all the elements, 
except fluorine, bromine, and the inert elements (helium, 
argon, neon, krypton, and xenon). Elements combined 
with oxygen alone give compounds called oxides. 

The burning of ordinary substances in the air, as wood 
and coal, is dependent upon the presence of oxygen in the 
air. Substances burn in pure oxygen much more rapidly 
and with more brilHance. The slow combination of oxygen 
with substances is spoken of as .oxidation, rapid combina- 
tion as coDibustion. When we add oxygen in, chemical 
union to a substance, we oxidize it. Iron takes oxygen 
from the air slowly in rusting. It does the same thing, 
but more rapidly, in pure oxygen at a low temperature. 
If heated first, it burns with great brilliancy, wdth the pro- 
duction of much heat. Just as much heat is produced in 
the three cases, but in the former two it is dissipated on 
account of the time factor, hence is not measurable. In- 
the three cases the iron is oxidized. 

Uses. Oxygen is used extensively for the production 
of heat in all processes of combustion. Oxygen may be 
breathed in the pure state for a time without injury, but 
the life forces acquire very much greater activity. Too 
long breathing of oxygen causes rapid cardiac action and 
the production of febrile condition. It is used in medicine 
for the treatment of pneumonia and anaemic conditions. 



32 GENERAL INORGANIC CHEMISTRY 

Ozone, O3. M. Wt, 48 

Schonbein, in 1840, ^accounted for the peculiar odor 
which is produced when an electric spark passes through 
oxygen or the air by the formation of ozone. The odor 
had been detected by Van Marum in 1785. 

Preparation. It is prepared by the passage of electric- 
ity through moist oxygen (up to about 5 per cent); by the 
slow oxidation of some substances, as phosphorus ; and 
recently in a more concentrated form by the action of 
ultra-violet light of wave lengths of 260 \x\x and shorter. 

It is found in the oxygen given off by plant leaves ; is 
produced in the oxidation of turpentine and probably by 
the beating of ocean waves upon the shores; and by elec- 
tric disturbances in the air. It readily decomposes into 
oxygen, but is sometimes found to the extent of o. i mg. 
in 100 1. of the air. 

Properties. It is a gas which possesses a peculiar odor, 
and in thick layers has a bluish color. Under a pressure of 
150 atmospheres or when cooled to — 184°, it condenses to 
an indigo-blue liquid (b.-p. — 1 16°). It is fifteen times as sol- 
uble in water as oxygen. At + 250-300°, or when exposed 
to light of wave lengths longer than 300 /-t/x, it is changed 
back to oxygen. It is half again as heavy as oxygen (sp. 
gr. 1.66). It is a powerful oxidizing agent, being known 
for a while as ''active oxygen." It oxidizes silver, which 
is unaffected by ordinary oxygen. It turns starch iodide 
paper blue, due to the liberation of free iodine by oxida- 
tion, which reacts with the starch to produce the color. 
It bleaches many dyes, which ordinary oxygen does not. 
When strong it irritates the air passages, even producing 
severe catarrh. Dilute, it serves to destroy organisms, 
hence purifies the air. 



OZONE 33 

It is used diluted, as found naturally in turpentine and 
hemlock districts, and is also artificially made in some urban 
sanatoriums, for the treatment of pulmonary diseases. In 
a concentrated form it serves to bleach oils and starch, steril- 
ize drinking water, and assist in the disposal of sewage. 

From the facts that ozone is made directly from oxygen, 
ozone decomposes to form oxygen, and is half again as 
heavy, we assume that its molecule is composed of three 
atoms, at least, of oxygen. This requires an assumption, 
which later will be shown to be correct, of the presence 
of two atoms of oxygen in a molecule of oxygen. When 
an element exists in two or more forms, as illustrated here 
and elsewhere (Chaps. XII, XVIII), the phenomenon 
is a case of allotropism. Usually there are some energy 
demonstrations in the changes from one form to the other. 
For instance, heat is absorbed when oxygen is converted 
into ozone (endothermic) and is evolved in the reverse 
process (exothermic) : — 

3 O2 = 2 O3 — 32,400 calories. 

Inasmuch as we may cause oxygen to form ozone or 
ozone to form oxygen, the reaction is spoken of as rever- 
sible, and may be indicated, 3 O2 :^ 2 O3. Many reactions 
are reversible. 

EXERCISES 

1. What are the principles illustrated by the methods given for 
the preparation of oxygen ? 

2. What is meant by an oxide? oxidizing a substance? 

3. Why do we say that the same amount of heat is produced in 
the combustion of iron in oxygen and in the formation of rust, as- 
suming that the product of the former reaction is the same as rust? 

4. Why may we assume the presence of at least two atoms in 
the molecule of oxygen? 



CHAPTER V 
WATER 

H2O. M. Wt., 18.016 

Hydrogen unites with oxygen to produce water. It 
occurs naturally in familiar abundance and widely distrib- 
uted, covering the larger portion of the earth and penetrat- 
ing its crust. It occurs as vapor in the air, from which it 
is condensed as dew or precipitated as rain, snow, and so 
forth. It constitutes a part of many minerals and chemicals. 
Three fourths of all living matter are water. In fact, it 
is absolutely necessary for the world's continuance as a 
habitable globe for us. An acre of green plants may 
evaporate 150 tons of water in a season. It is the best 
known chemical compound and essential for many chemi- 
cal changes. Its study is therefore of the utmost 
importance from a scientific, as well as practical, stand- 
point. 

Water, as ordinarily seen, especially as a deep layer in 
large bodies, has a blue or greenish blue color. Such 
water is impure. It is purified by distillation. The 
apparatus used for making distilled water, which is pure 
enough for ordinary laboratory purposes, is constructed of 
tin, copper, or glass. The purest water cannot be kept for 
any length of time in glass vessels, because some of the 
constituents of glass are dissolved, and they render the 
water impure. The purest water is made in apparatus 
constructed of materials thp least affected by water, for 
example, platinum or quartz. The first portion of the 

34 



WATER 35 

distillate is discarded, and only the middle portion is 
collected. 

Pure water is a colorless liquid between o° and + ioo° 
and has an insipid taste. As the temperature is lowered 
it becomes denser, showing the greatest density at + 4° ; 
below that point it expands till it freezes at zero. This is 
the reason why water freezes at the top and not the bottom 
of our lakes and streams; for the water, being less dense 
at the freezing point than at + 4°, remains on the surface. 
When water changes into ice, 100 volumes of water ex- 
pand to 109 volumes of ice (sp. gr. 0.9173), which floats. 
Water crystallizes in rhombohedra of the hexagonal sys- 
tem. Under a pressure of 1000 atmospheres water solidi- 
fies at — 7°. Water begins to dissociate into hydrogen 
and oxygen at + 1000°; the dissociation is complete at 
+ 2500°. One volume of water at + 100° is changed into 
1696 volumes of steam. The specific gravity of steam is 
0.622. One liter of aqueous vapor at + 100° and 760 mm. 
pressure weighs 0.59 g. The latent heat of ice is 79 
calories ; the latent heat of steam 536.4 calories. 

In studying the composition of any substance, we have 
four objects in view; namely, to learn (i) of what it is 
composed, that is, its qualitative composition ; (2) how 
much of each element is present, that is, its quantitative 
composition; (3) how many atoms are in the molecule, 
that is, the molecular weight ; and (4), if it is a compound, 
how the atoms are associated in the molecule. 

At this point in determining the composition of water, 
it is convenient to consider only the first two objects. It 
is desirable, almost necessary, before drawing final con- 
clusions, not only to analyze, but to synthesize a substance 
as well. The study of the composition of water is given 
in some detail as an illustration of methods of procedure 
in scientific investigations. 



36 GENERAL INORGANIC CHEJVIISTRY 

Qualitative Composition 

First, we have seen that metals break up water and give 
off hydrogen. 

Second, by the electrolysis of water, we obtain hydrogen 
and oxygen. As pure water has not been decomposed by 
the electric current, these gases might be attributable to 
the acid or alkali added (in fact, we know they are not); but. 

Third, hydrogen when burned in oxygen forms water. 

Therefore, it appears that water contains only hydrogen 
and oxygen. To prove it, however, we determine its 

Quantitative Composition- 
First, by electrolysis, we learn that we obtain two vol- 
umes of hydrogen and one volume of oxygen from water : 

Water = 2 H + i O. 

Seco7id, if we mix two volumes of hydrogen and one of 
oxygen and cause them to combine by passing an electric 
spark through the mixture, we obtain water. If we have 
an excess of either gas beyond this ratio, 2:1, that excess 
remains in the apparatus unchanged (law of definite pro- 
portions). We may weigh the gases and thus determine 
the weights of each involved in the synthesis, but it is an 
inconvenient and difficult procedure. We therefore con- 
firm the above. 

Third, by passing hydrogen, free from water, over a 
metallic oxide which is heated. Black copper oxide, when 
treated in this manner, gives up its oxygen to the hydro- 
gen, forming water, and assumes the color characteristic 
of metallic copper : 

Copper oxide + hydrogen = water -f- copper. 



WATER 



37 



If we subtract the weight of copper after the experi- 
ment from the weight of the copper oxide before the ex- 
periment, we obtain the weight of the oxygen taken by 
the hydrogen to form the water. This weight subtracted 
from the weight of the water collected gives the weight 
of the hydrogen necessary to combine with the oxygen to 
produce that amount of water. The data thus secured 
show us that eight parts by weight of oxygen combine to 
form nine parts by weight of water. One part by weight of 
hydrogen is needed, and the ratio by weight of oxygen 
and hydrogen in water is 8 : i. But we have seen that two 
volumes of hydrogen combine with one volume of oxygen 
to produce water, and it is necessary for us to harmonize 
these facts in any interpretation we may make. 

From the gas laws we know that all gases, within 
reasonable limits, expand or contract for equal increments 
of heat and similar variations in pressure. Therefore, 
gases exist as free-moving molecules, and equal volumes 
of gases under like conditions of temperature and pres- 
sure contain an equal number of molecules. This is the 
reasonable explanation offered by Avogadro in 1827. It 
matters not what is the composition of the molecules, 
whether they are single atoms or contain a large number 
of atoms. 

The simplest assumption regarding the hydrogen mole- 
cule, and so far data have not been presented in these 
pages which warrant any other, is that it contains one 
atom. As two volumes of hydrogen require only one 
volume of oxygen to produce water, the ratio becomes a 
multiple; that is, 2 : 16 instead of i : 8. By definition half 
atoms cannot enter our considerations, and as we have 
learned (p. 33) that the oxygen molecule contains at least 
two atoms, we conclude that the oxygen atom bears an 



38 GENERAL INORGANIC CHEMISTRY 

equivalent weight relative to the hydrogen atom of 8 : I. 
If, by convention, the lightest known atom (hydrogen) is 
placed at i, we may say that the atomic weight of oxygen 
is 8. In fact, using round numbers, it is i6. The reasons 
for arriving at the latter figure, which is now given to avoid 
a temporary wrong impression, will be seen later (p. 52). 

EXERCISES 

1. Upon what theoretical considerations does the distillation 
of water depend? Why should the first portion of the distillate 
be discarded in preparing the purest water? 

2. Why do lakes and other natural bodies of water freeze at 
the top? 

3. How is the composition of water proven ? 

4. How much copper oxide would be used and copper obtained 
in preparing 3.2 g. of water? 



CHAPTER VI 
WATER — PRACTICAL CONSIDERATIONS 

Water is nature's great solvent. All substances are 
more or less soluble in it. Therefore, when naturally 
found it is never pure. Rain-water contains dust, nitrogen, 
oxygen, and carbon and other compounds, many of which 
are fortuitous. Much of it sinks into the earth and issues 
again in the form of springs and rivers, containing differ- 
ent mineral constituents, depending upon the minerals 
with which it has come in contact. Hard water, — tempo- 
rary and permanent, — contains calcium and magnesium 
salts. The waters from mineral springs are given names 
according to certain constituents which they may contain, 
as iron (chalybeate), alum, hydrogen sulphide (sulphur), 
salts (saline), lithium compounds (lithia), carbonic acid 
(acidulated), and so forth. Waters with these various con- 
stituents eventually reach the oceans or some inland lake. 
There they evaporate with a constant accumulation of the 
non-volatilized solids, for the evaporated water is again 
precipitated, as rain, snow, and so forth, scours the land, 
and returns to the oceans laden with another burden of 
variegated suspended and dissolved matter. Sea water 
contains 2.7 per cent of sodium chloride (salt) with a total 
of 3.5 per cent of solid matter. Some of the salt lakes 
contain a much larger percentage. 

In making steam these solids accumulate within the 
boilers and constitute a frequent source of grave annoy- 
ance unless removed. They sometimes form solid cakes 

39 



40 GENERAL INORGANIC CHEMISTRY 

and produce what is known as boiler scale. The scale is 
not a good conductor of heat, so the efficiency of the 
boiler is affected, often seriously. The metal and the scale 
have different coefficients of expansion. If the water gets 
too low in the boiler, the metal becomes overheated and 
expands away from the hard scale, which often cracks. 
If fresh water is run into the boiler, the scale, quickly 
cooled, cracks and brings water directly in contact with 
the superheated metal and underneath the scale. A large 
volume of steam is suddenly generated, some of the water 
even being decomposed perhaps. Unusual pressure is 
produced, often with consequent explosion. 

The most important practical problem for any commu- 
nity is the provision of a satisfactory supply of potable 
water. With congestion of population filth accumulates 
on and in the soil. Water which has come in contact with 
these sources of contamination and is subsequently drunk 
propagates disease. Mortality diminishes when potable 
water is supplied, but increases after an interval unless 
provision is made for the disposal of the sewage. 

Three factors are involved in determining the potability 
of a water and accepting it as a constant supply. First, 
regular bacteriological examinations should be made to 
determine the presence of pathogenic (disease-producing) 
bacteria. Second, frequent chemical examinations of the 
water should be made to determine the presence of food 
(nitrogenous organic compounds) upon which the bacteria 
live and propagate. The bacteria cannot exist long in 
media which are not provided with their food. The 
determination of their presence in water one day does not 
indicate their continuance, unless the chemical examination 
shows the presence of their food. A chemical examination 
may show the presence of bacterial food and also products 



WATER — PRACTICAL CONSIDERATIONS 41 

resulting from their thriving upon that food (presence of 
free ammonia, nitrites, and nitrates), which means that the 
water is suspicious and should be avoided, but it does not 
prove that the bacteria present are disease-producing. 
There are beneficial bacteria and harmful bacteria. The 
former cause, through processes termed nitrification (oxi- 
dation) and denitrification (reduction or de-oxidation), the 
compHcated carbon compounds of nitrogen in water and 
the soil to be reduced to simpler compounds, harmless in 
their diluted condition, as far as the production of disease is 
concerned, and most useful, in fact essential, in providing 
food for plants. This shows how closely chemistry and 
biology are associated. Third, a regular systematic survey 
should be made of the sources from which the water is 
obtained. By these means a temporary or permanent con- 
tamination of the w^ater may be determined and proper 
steps taken to avoid the evil consequences of using it. No 
citizen can have these facts too well impressed upon him. 
He need not, however, concern himself with the details by 
which the information is obtained, for they involve techni- 
calities known only to the expert in such matters. 

As an adequate supply of water sufficiently .pure is 
difficult to secure for a large community, except at great 
expense, it becomes necessary at times to use a fairly im- 
pure water and render it potable. Most bacteria, or their 
spores, cease to live at the temperature of boiling water. 
It is safe, therefore, when the potability of water is in 
question, to boil it. Doing this on a large scale, however, 
is out of the question on the score of the expense involved. 

Water may contain suspended or dissolved impurities. 
The former are removed by filtration, provided the pores 
of the filtering medium are sufficiently small. A Pasteur 
filter is made of unglazed porcelain and has very small 



42 GENERAL INORGANIC CHEMISTRY 

pores. When this is attached to the pipe, the water is 
forced through by its own pressure and the ^fine parti- 
cles are held back. These soon form a sHmy coating 
which practically prevents the passage of the liquid. 
This slime may also become a breeding bed for the 
bacteria, so it should frequently be removed and cleaned. 
On a large scale the filter is usually made of sand, the 
grains of which, lying upon each other, give considerable 
porosity. Very finely divided particles (clay soil is made 
up mainly of particles less than 0.005 ^^- i^ diameter) are 
often not removed when water passes through a sand 
filter ; nor are the bacteria, which are even smaller. A 
jelly, which is more or less agglomerated, does not pass 
through the pores. If we agitate the water with a gelati- 
nous material, these particles, even the bacteria, are more 
or less attached and then are held back by the filter. 
This is accomplished practically by adding something to 
the water which subsequently forms the desired jelly. 
Alum is a compound of some complexity, which on being 
added to water in small amounts dissociates^ that is, breaks 
up into simpler substances. As water brings about this 
dissociation, we speak of the phenomenon as hydrolysis ^ 
It plays a very prominent part in many chemical actions. 
One of the dissociation products of alum is a white jelly 
[aluminum hydroxide, A1(0H)3]. 

Another method of treating water is to impound it and 
make the conditions most favorable for the propagation of 
the bacteria. They develop very rapidly and soon ex- 
haust the food available, producing harmless substances, 
and die through starvation. Or, the bacteria are killed by 
the addition of a poison (in very small amounts), which, 
after it has done its deadly work, gradually decomposes or 
combines with something else. Water so treated becomes 



WATER — PRACTICAL CONSIDERATIONS ' 43 

harmless when taken into the animal system. Some of 
the substances used for this purpose are ozone, chlorine, 
and copper sulphate. The last named has recently come 
into extensive use, as it also kills certain vegetable growths 
(algae). These plants grow in abundance in -some ponds 
or lakes, where drinking water is collected, and often give 
the water objectionable color or odor or taste, and pro- 
duce disease. 

EXERCISES 

1. Explain the formation of boiler scale. 

2. Outline the main considerations involved in determining the 
potability of water. 

3. Give and explain the principles put into practice in render- 
ing water potable. 



CHAPTER VII 
WATER — THEORETICAL CONSIDERATIONS 

When a gas is liberated in a closed vessel which has 
been evacuated, it spreads itself throughout the volume of 
the containing vessel. It occupies the space, as it were, 
and exerts a pressure upon the restraining walls. All gases 
do this, it matters not what is the composition of the 
molecules. The distribution is uniform, and presumably 
the same number of molecules are in. equal volumes 
(Avogadro's hypothesis). Similar conditions of tempera- 
ture and pressure must obtain, to be sure, but the gas re- 
tains its chemical individuality. When we bring together 
two volumes, one each, of different gases, which do not 
form a chemical combination under the prevaihng con- 
ditions, we find that the particles of each gas distribute 
themselves uniformly through the new volume. The 
mixed gases exert a combined pressure, made up of the 
pressures of the two, acting independently of each other. 
Each gas therefore exerts 2, partial pressure. 

When we place a solid (salt) in a liquid (water), there is 
a tendency on the part of the solid particles to enter the 
liquid. The pressure created by the molecules of the 
solid is known as sohUion pressure. A time arrives when 
this pressure is equaled by the pressure created by the 
particles in solution trying to return to the solid. There 
is equilibrium at that temperature. The excess of the 
solid remains behind, and we have a saturated solution. 
The solute distributes itself uniformly throughout the 

44 



WATER — THEORETICAL CONSIDERATIONS 45 

volume of the solvent, so the liquid acts as a medium 
through which the molecules occupy the volume of the 
liquid. The solubilities of different substances are not 
the same, hence we do not get the same number of mole- 
cules in equal volumes of the saturated solutions of differ- 
ent substances. To be sure, we do get a definite quantity 
of the solute in solution for each temperature,* but this 
quantity bears no atomic relationship to the solvent, hence 
we do not look upon the solution as a normal chemical 
action which involves breaking into the molecule. Yet the 
physical individualities of the substances dissolved are 
sometimes changed. Also in particular cases we do get a 
change, such as we observe in hydrolysis. 

In a measure, the presence of one solute does not inter- 
fere with the presence of another. We may mix a saturated 
sodium chloride solution with a saturated sodium carbonate 
solution, both in water. Or, putting it another way, if we 
have one solution, say, of sodium chloride about half 
saturated, and place in it an excess of the carbonate, the 
hquid will take up enough of the carbonate to saturate that 
part of the water beyond the amount necessary to make a 
saturated chloride solution for the amount of chloride 
present. Each exerts its partial pressure, as in the case of 
the gases. 

The solubility of a solute in different solvents is usually 
different. If, therefore, we have two immiscible solvents 
mixed, the solute distributes itself in each, according to the 
specific solution tension. An illustration will make this 
clear. Iodine is not very soluble in water, yet we may 

* In some cases we obtain a liquid which has in solution more of the solute 
than it normally holds at the special temperature. This we call stipersatura- 
tion. The solution is in unstable equilibrium. As soon as the liquid is dis- 
turbed, by the introduction of a tiny crystal or a particle of dust, the excess 
of the solute separates at once. 



46 GENERAL INORGANIC CHEMISTRY 

make a saturated solution. Iodine is very soluble in ether. 
Water and ether are so limited in their solubility in each 
other, that we say they are immiscible. If we mix the 
water solution of iodine with ether, most of the iodine goes 
into the ether, but not all. The iodine distributes itself 
according to its solution pressure with each solvent {Law 
of Partition). This process is called extraction, and is one 
extensively used in chemical practice. 

Each solvent dissolves a definite amount of each solute 
at a fixed temperature. The amount of gas dissolved 
decreases with the elevation of temperature. The reverse 
is usually the case with soHds ; for example, lOO parts of 
boiling water dissolve 360 of alum, whereas 100 parts of 
cold water dissolve only 10 parts of alum. If a saturated 
solution is made at + 100° and then is cooled to a lower 
temperature, the excess above the amount equal to the solu- 
bility at the lower temperature will ordinarily separate 
out, in this case, as crystals. The molecules must be in a 
mobile condition, and when they have time for settling, 
they tend to arrange themselves into masses often bounded 
by definite planes which form regular angles. 

The phenomenon of aystallization may be brought 
about by (i) evaporation of a portion of the solvent, (2) 
by melting a solid without using any solvent, or (3) by 
sublimation. The essential conditions are freedom of 
movement of the particles and time for their assumption of 
definite forms. 

There are six basic forms according to which crystals 
are classified : — 

1. Regular or isometric system with three axes, all 
equal and at right angles to each other. 

2. Quadratic or tetragonal system, one of the three axes 
is of a different length. 



WATER — THEORETICAL CONSIDERATIONS ' 47 

3. Rhombic, all axes unequal but at right angles. 

4. Monoclinic, all axes unequal, only two at right angles. 

5. TricUnic, all axes unequal, all oblique, none at right 
angles. 

6. Hexagonal, three axes in one plane forming equal 
angles (60°), a fourth at right angles to that plane. 

By the evaporation of simple solutions we recover the 
solute, in some cases unchanged. In others all the solute 
is there, but it has appropriated a definite amount of the 
solvent, which gives the residue properties different from 
those of the original solute. Hence, in the simple solution 
we may have indications of physical and chemical changes. 
An illustration will render this clearer. When water is the 
solvent and salt is the solute, on evaporation we obtain 
the crystals characteristic of the sodium chloride. If we 
dissolve dry soda (sodium carbonate) in water and evapo- 
rate the solution, we get crystals composed of soda plus 
ten parts of water. By slight heat the water is driven off 
and the clear crystals immediately crumble into a powder, 
the same as originally dissolved, and give the appearance 
of losing their crystalline form. A more striking illustra- 
tion is had when a solution of copper sulphate (bluestone) 
is evaporated. Large blue crystals are obtained, which 
contain hydrogen, copper, oxygen, and sulphur in the pro- 
portion to give the formula CuHj^SOg. In making the 
analysis, however, it is observed that by heating we may 
drive off hydrogen and oxygen to the extent of 5 H2O and 
collect it directly as water. The blue color of the crystal 
disappears. For these reasons, namely, loss of crystalline 
form, color, and so forth, the water present has been com- 
monly referred to as ivatcr of crystallization, and the for- 
mula of this particular substance may be written, CuSO^, 
5 H^O. 



48 GENERAL INORGANIC CHEMISTRY 

In point of fact, this is incorrect, because the water 
present is just as much a part of the molecule as the soda 
or copper sulphate. When the water is removed in part 
or entirely, the particular crystalline form is changed. 
Progressive thought teaches that all solids are crystaUine. 
We do have solids which appear without crystalline form, 
— afnorphoiLS substances, — but they are supercooled 
liquids. The water taking part in the formation of a 
definite crystal form enters as a molecular compound. 
These compounds may properly be spoken of as hydrates. 

There are other substances which, when dissolved in 
water, combine with it in a different manner from that 
just referred to. We may illustrate this by an example, 
but a study of the substances involved must be postponed 
to a more appropriate time. Sodium oxide dissolves in 
water according to the formula, 

Na20+ H20=^2 NaOH, 

and we have a real chemical solution, for on evaporation 
we secure the solid NaOH or 2 NaOH. The NaOH 
dissolves, however, forming a simple solution. On ac- 
count of the OH, these compounds of water are called 
hydroxides (a word derived from hydrogen and oxygen). 
This particular one (sodium hydroxide) does not yield 
water on heating, but many of them do ; for example, 

2 CuOH:±Cu20 + H2O. 

Although we obtain water on heating hydrates and 
hydroxides, the water is present in an extramolecular 
union in the former and intermolecular union in the 
latter. 

The particles of evaporating water pass off in the gas- 
eous state. This is a property of all liquids. The rate 



WATER— THEORETICAL CONSIDERATIONS 49 

at which the particles leave is defined by the gaseous pres- 
sure they exert and is known as the vapor pressure of the 
substance under the particular conditions. If a vessel is 
partially filled with a liquid and closed, the vapor pres- 
sure soon reaches a maximum, which is definite for each 
temperature. The pressure is independent of the amount 
of liquid present, provided there be enough to produce 
sufficient vapor to create the pressure for the particular 
temperature. If there is too little of the liquid, it is all 
changed into a gas and the maximum pressure is not at- 
tained. If the gas above the liquid is compressed, the 
temperature remaining constant, a portion at once returns 
to the liquid state, as more than the maximum pressure 
cannot continue. The pressure of the gas is dependent 
upon the number of molecules in each unit of space. 
The pressure increases with increase of temperature. The 
maximum pressure at any temperature is known as the 
vapor tension of the liquid at that particular temperature. 
Aqueous tension at 0° will support a column of mercury 
4.6 mm. high; at 20°, 17.4mm.; and at 100°, 760 mm., 
when the water boils. When water is under an atmos- 
pheric pressure of 680 mm., it boils at + 97°; 800 mm., at 
+ 101.4°. When the space above water has taken up all 
the vapor allowed by the aqueous tension at a particular 
temperature, it is said to be saturated. It will thus be 
seen that the aqueous tension is independent of the size of 
the space and the amount of water, provided there is an 
excess. It is even independent of the presence of other 
gases, and is dependent solely upon the ability of the water 
to produce a vapor. The humidity of the air varies. It 
is usually about two thirds saturated. 

Solid hydrates, as those referred to, tend to give off the 
combined water in the form of a vapor, as ice does. 



50 GENERAL INORGANIC CHEMISTRY 

Crystals of sodium carbonate with ten molecules of water, 
or sodium sulphate with ten molecules of water (Glauber's 
salts), on exposure to the air lose water and crumble down 
to a white powder. We speak of this as efflorescence. If 
the crystals are placed in a stoppered bottle, they con- 
tinue to give off water. After a lapse of time, however, 
the vapor pressure reaches the maximum, and no more 
water is given off. The crystals retain their characteristic 
form. Each hydrate possesses a definite vapor pressure. 
When the vapor tension is less than the aqueous ten- 
sion of the air, the crystal retains its form. As stated, the 
aqueous tension at 20° is 17.4 mm., and ordinarily the pres- 
sure in the air is about 12 mm. (two thirds). Copper sul- 
phate with five molecules of water exerts a pressure of 6 
mm. at 20° ; consequently, its crystals remain unchanged 
on exposure to the air. 

EXERCISES 

T, Trace the relationship between the partial pressure of gases 
and the solution pressure of solids. 

2. Explain the law of partition. 

3. What are the six basic forms of crystals and the conditions 
favorable for crystallization? 

4. What is the explanation of vaporization, and upon what 
factors is it dependent? 

5. Explain what is meant by a hydrate; hydroxide; efflo- 
rescence. 



CHAPTER VIII 
THE HALOGENS 

The solid obtained from evaporated sea water is a mix- 
ture of a number of compounds, the most prominent of 
which is sodium chloride. When this is treated with an 
acid, as sulphuric, a gas is given off, a water solution of 
which is known as hydrochloric acid (see next chapter). 
The gas is hydrogen chloride. 

If hydrogen chloride is liquefied and has a direct current 
of electricity passed through it, two gases of equal volumes 
are obtained. One is colorless hydrogen, evolved at the 
negative pole ; and the other is yellowish green chlorine, 
given off at the positive pole. Although it was discovered 
by Scheele in 1774, Humphry Davy proved the elementary 
nature of chlorine in 18 10 and named it. 

If hydrogen and chlorine are brought together, they 
unite with explosive violence (either when heated or on 
exposure to bright hght) to re-form the hydrogen chloride. 
We find one volume of hydrogen requires one volume 
of chlorine. After the union we have two volumes of 
the hydrogen chloride.* Gay-Lussac (1808) laid down a 
simple law of combining volumes ; namely, whenever gases 
nnite, or ivJienever gaseous products result from the 7mio7t, 
the volumes involved can be represented accurately by ratios 
of small integers. 

* The measurements are made under similar conditions of temperature and 
pressure, and unless otherwise stated all measurements of gases are to be con- 
sidered as made at o^ and 760 mm. pressure. 

51 



52 GENERAL INORGANIC CHEMISTRY 

This may be readily illustrated by diagrams : — 







I volume 
hydrogen 


+ 
+ 


I volume 
chlorine 


= 


2 volumes 
hydrogen chloride 


md 












2 volumes 
hydrogen 


I volume 
oxygen 


= 


2 volumes 
water (steam) 



The ratios for hydrogen chloride are i : i : 2, and for 
water 2:1:2. 

According to the explanation of Avogadro, and we 
have no better, we have equal numbers of molecules in 
equal volumes of gases (under the same conditions of tem- 
perature and pressure). If we assume that each single 
volume contains 1000 molecules, then we have 2000 
molecules of hydrogen chloride. There can be no case 
of partial pressure {(/.v.) here, as chemical combination 
has taken place. The composition of hydrogen chlo- 
ride calls for at least one atom each of hydrogen and 
chlorine, as half atoms are excluded by definition. As 
there are 2000 molecules of hydrogen chloride, there must 
be at least 2000 atoms of hydrogen in the 1000 molecules 
of hydrogen. Hence, each molecule of hydrogen must 
contain at least two atoms. The same is true for the chlo- 
rine and oxygen. Therefore, we confirm the statement 
that the atomic weight of oxygen is 16, not 8, and we may 
write the formula for the electrolysis of hydrogen chlo- 
ride : — 

2Hci:|:h2 + ci2. 

This is one of the methods by which the number of 
atoms in a molecule may be determined. It is applicable 
only to the gaseous state, however. 



THE HALOGENS 53 

In order to eliminate intermediate steps from the raw 
product to the finished material, practical men applied the 
principle of electrolysis directly to the sodium chloride in 
solution : — 

2 NaClz^Na2 + CI2. 

The reaction is, in fact, more complicated than shown 
in this equation, but chlorine is now obtained free in large 
quantities in this manner. 

Of considerable historical interest and theoretical im- 
portance is the method used by Scheele in the discovery 
of chlorine. If hydrogen is removed from hydrogen chlo- 
ride, chlorine is obtained free. In oxidizing a substance, 
at one time, we were supposed to introduce oxygen into 
the compound. We may oxidize a substance, however, by 
taking hydrogen away from it. We know that hydrogen 
readily combines with oxygen, so we may oxidize hydrogen 
chloride with an agent like manganese dioxide. We get 
an equation : — 

X HCl + y Mn02 = i^ Y\^0 + w MnCl2 + a CI. 

We must learn certain facts by actual experimentation 
before we can write out what takes place in any chemical 
reaction. After we have learned how many reactions pro- 
ceed, we may predict, often with accuracy, the course of an 
unknown reaction. We may study this particular equation 
and opportunely learn a method by which an equation may 
be determin.ed. From the experiment we know that a 
mixture, as shown on the left side of the equation, gives 
us the three substances shown on the right. We should 
anticipate this, because Mn02 decomposes on heating, giv- 
ing off oxygen. Scheele, in 1775, prepared oxygen in this 
manner. We should expect a compound Hke MnOg, in 



54 GENERAL INORGANIC CHEMISTRY 

which all the oxygen had been replaced, by chlorine, to 
break up with the separation of the latter element. That 
fact is stated in the equation. But how much of each con- 
stituent takes part ? We have learned that 2 H combine 
with I O in water (H2O). For all the O in i (j) MnOg, 
we require 4 H. The value of z becomes 2. In hydrogen 
chloride we have one each of H and CI. Therefore, x = <\. 
If we analyze the manganese chloride obtained, we secure 
the formula MnC]2. As only i Mn enters, zv ~ i, and as 
4 CI are involved, we have two left over, which gives our 
value for a. Hence we write the equation : — 

4 HC1+ Mn02:::^2 H^O + MnCl2 + JCI2. 

The principle of oxidation is extensively used in chemi- 
cal processes. Many other oxidizing agents have been 
and are used for the preparation of the chlorine from HCl, 
but the reactions are quite complicated. One of the sim- 
plest, as it appears in the following equation, is to use 
oxygen itself : — 

4 HC1+ 02^2 H2O + 2 CI2. 

Chlorine decomposes water, especially under the in- 
fluence of light, according to the above equation, reading 
from right to left. The double arrow indicates that we 
are dealing with a i^evei^sible reaction — one preponderat- 
ing to the right under certain conditions and the left 
under another set of conditions. In order to cause it 
to go from left to right, it is necessary to have the 
proper conditions and something there to do it. In this 
particular case, it is necessary to have a temperature be- 
tween 370° and 400°. The material used is pumice (to 
present a large surface), which has been soaked in a solu- 
tion of copper chloride. Any material which by its pres- 
ence facilitates a reaction in any one direction is spoken of 



THE HALOGENS 55 

as a catalytic agent. The process is called catalysis. The 
contact agent (catalyzer) may or may not undergo change 
while the reaction is in progress, but it retains its initial 
integrity at the end of the reaction. Catalysis plays a 
very important part in many chemical changes. 

Along with the chlorides are similar compounds of 
bromine and iodine, but in very much smaller amounts. 
Certain plants, like seaweed, concentrate iodine. In fact 
this occurrence led to its discovery by Courtois, who used 
the ashes from burned sea-weed in making soap. In 1895 
Bauman found 9 per cent of iodine in the purified ex- 
tract from the thyroid gland. 

Bromine and iodine are prepared by any of the methods 
given for chlorine, but more usually by the manganese 
dioxide process. As chlorine, bromine, and iodine separate 
at the positive pole, they are electro-negative, but to differ- 
ent degrees. Chlorine is more strongly electro-negative 
than bromine, as that element is correspondingly stronger 
than iodine. The more pronounced electro-negative ele- 
ment will displace the weaker. This fact is taken advan- 
tage of in separating these elements. 

2 NaBr + CI2 r^ 2 NaCl + Brg, 
and 

2 Nal H- Cl^-^ 2 NaCl + I2. 

These equations illustrate the principle of substitution, 
which is extensively applied in chemistry. 

The comparable properties of these three elements are 
given in the table. All have characteristic, penetrating, 
disagreeable odors. With increase in atomic weight the 
physical state, at ordinary temperatures, changes from that 
of a gas to a solid. Chlorine is soluble in water, hence is 
collected by air displacement. The '' solid bromine " of 



56 GENERAL INORGANIC CHEMISTRY 

commerce is siliceous earth more or less saturated with the 
liquid. These elements are not combustible, nor do they 
combine easily with oxygen. Indirectly oxygen forms 
compounds with chlorine and iodine, but none with bro- 
mine is known, although compounds of bromine, hydrogen, 
and oxygen are made. They readily combine with hydro- 
gen (halogen acids) and the metals. Hydrogen and some 
metals burn in chlorine, as they do in oxygen. The attrac- 
tion chlorine exhibits for hydrogen is so great that it will 
remove that element from many of its compounds ; for 
example, under the influence of sunlight, it decomposes 
water : — 

H20 + Cl2Z^2 HCl-f O. 

It will be observed that but one atom of oxygen in the 
molecule is indicated. This is supposed to be the case 
for the instant, but not for any length of time, as the 
final oxygen obtained shows two atoms in the molecule. 
When an element is had thus temporarily in the free or 
nascent condition, it is more active than when it exists as 
the normal molecule. Colored cloth exposed to ordinary 
oxygen is not affected. It is bleached by nascent oxygen. 
Chlorine destroys many colors. The bleaching action is 
attributed to the liberation of nascent oxygen, for the ob- 
jects must be wet. Concentrated water solutions of chlo- 
rine and bromine, when cooled, give crystals Cl2,ioH20, 
and Br2, 10H2O. Charcoal absorbs 200 times its volume 
of chlorine. 

For other reasons than similarity of occurrence we may 
consider the element fluorine at this point. It has never 
been found in nature as the free element, but always com- 
bined with some metal in salts, as fluorspar (calcium 
fluoride, CaF2) and cryoHte (aluminum sodium fluoride, 



THE HALOGENS 57 

AIF3, 3 NaF).* Small amounts are found in bones and 
the enamel of teeth. 

While desirable, it is not necessary that the element is 
actually isolated that we may be convinced gf its existence. 
Fluorine was known and accepted as an element for 
seventy-five years before it was obtained free from other 
elements. This Moissan accompHshed (1886) by the elec- 
trolysis of anhydrous liquid hydrogen fluoride (at — 23°) in 
vessels made of copper, coated on the inside with copper 
fluoride, which is not affected by free fluorine. The elec- 
trodes were made of platinum and iridium, as other metals 
combine at once with fluorine. Pure hydrogen fluoride 
does not conduct the current, and fluorine decomposes 
water instantly, so a little potassium fluoride (KF) was 
added to facilitate the flow of electricity. 

Fluorine compounds with all the accepted elements, 
except the helium group of gases, oxygen, chlorine, and 
bromine, are known. It is the most energetic of the 
electro-negative elements. It replaces chlorine in its com- 
pounds, as that element displaces bromiine and iodine. 
It attacks all compounds of silicon, as glass or porcelain, 
except when perfectly dry. A drop of water brought in 
contact with fluorine is decomposed at once to produce 
ozone : — 

3F2+3H20z±:6HF-f O3. 

Its action on organic material is extremely destructive, 
hence it is a dangerous substance to experiment with. 

All four of these elements in the gaseous condition are 
irritant poisons. In the liquid condition they are corro- 
sive poisons. An alcoholic solution of iodine is used as a 
counter-irritant in medicine. Chlorine and bromine are 

* This formula may be written NasAlFg. 



58 



GENERAL INORGANIC CHEMISTRY 



powerful disinfectants. The former is used extensively 
for that purpose, but the coloring agents in curtains, car- 
pets, and so forth, are destroyed. They, chlorine espe- 
cially, are used for bleaching. Under six atmospheres of 
pressure chlorine is converted into a yellow liquid and is 
transported in steel cylinders. 

If they are liberated they quickly form compounds, hence 
they do not occur free in nature, but mainly as binary 
compounds with metals, as CaFg (calcium fluoride), NaCl 
(sodium chloride), MgBr2 (magnesium bromide), or KI 
(potassium iodide). They are called halogens, or "salt- 
producers." 

TABLE OF THE COMPARABLE PROPERTIES OF THE 
HALOGENS 



Element . . 




. Fluorine 


Chlorine 


Bromine Iodine 


Derivation of name 


fluo = 
to flow 


yellowish green 


a stench 


ioetSr;? 
violet-form 


Symbol . . - 


F 


CI 


Br 


I 


Atomic weight 


, 


19.0 


3546 


79.92 


126.92 


Discoverer . 




. Ampere* 


Scheele 


Balard 


Courtois 


Date . . . 




1810 


1774 


1826 


1811 


Physical state f 




gas 


gas 


liquid 


solid 


Appearance . 




colorless 


greenish 


red 


metallic § 




(nearly) 


yellow 




crystals 


Specific gravity 


.... 


2.45 


5-52 


8.7 


Boiling-point . . 


-187° 


- 33-6^ 


+ 59'^ 


+ 184.3° 


Melting-point . . 


-223^ 


-102° 


-r 


+ 114° 


Specific gravity, liquid 


I-3I 


1-33 


3-i8 




Specific gravity, solid 




.... 


.... 


4-95 


Solubility in water 


decomposes 


it I : 2.6 vol. 


1:30 


I : 3600 


Color with stare 


h . . 


none 


none 


yellow 


blue 



* Long known in compounds, as fluorides, CaF2. Moissan first isolated the 
element in 1886. 

t At ordinary temperature, + 20°. 
§ The vapor is violet. 



THE HALOGENS 59 

EXERCISES 

1. How do we confirm the atomic weight of oxygen as 16? 

2. Write the equation for the production of bromine from hy- 
drogen bromide, using manganese dioxide. 

3. How much potassium iodide (KI) would be needed to pro- 
duce 4.3 g. iodine? 

4. What three principles are illustrated in the preparation of 
the halogens? Write an equation for each. 

5. Explain the bleaching action of chlorine. 

6. Can we use the oxidation method (manganese dioxide) for 
the preparation of fluorine from hydrogen fluoride (HE)? If not, 
why not ? 



CHAPTER IX 
HALOGEN ACIDS 

The halogens form compounds with hydrogen, HCl, 
HBr, HI, and HF, the comparative properties of which 
are seen in the table. They are all colorless gases, with 
penetrating and suffocating odors, poisonous, neither com- 
bustible nor supporters of combustion, but extremely sol- 
uble in water. These solutions are called acids, and are 
corrosive. Their attraction for water is shown by fuming 
in the air, the moisture of which absorbs them. They can- 
not be collected over water. The gases and their water 
solutions possess strong attraction for metals and their 
compounds, hence are not found free in nature. Hydro- 
gen chloride, however, occurs in certain volcanic gases and 
the waters flowing from the neighborhood of these vol- 
canoes, but as it combines readily with other substances, it 
does not remain free long. Hydrogen chloride also exists 
(0.08 per cent) in loose combination with certain compli- 
cated compounds in the gastric juice, where it plays an im- 
portant part in the processes of digestion. 

Basil Valentine, in the fifteenth century, first produced 
hydrogen chloride, called at different times marine or 
miLriatic acid, by heating a mixture of ferrous sulphate and 
sodium chloride. Priestley, in 1772, isolated the gas, and 
Davy, in 18 10, proved that it did not contain oxygen. 

Hydrogen chloride is called hydrochloric acid when dis- 
solved in water. It may be prepared by the direct union 
of the elements: H2 + Clg — 2 HCl. These gases may be 

60 



HALOGEN ACIDS 6l 

safely mixed in the dark, but a violent explosion results 
when the mixture is exposed to heat or bright light. Such 
mixtures are usually prepared only for demonstration pur- 
poses, and must be avoided in the laboratory. Hydrogen 
burns quietly in an atmosphere of chlorine, and chlorine 
burns in hydrogen. Hydrogen chloride is produced in 
either event. This fact has recently been applied techni- 
cally with success. 

The usual method followed depends upon the interaction 
of sodium chloride (salt) and sulphuric acid (oil of vitriol) : 

NaCH- H2S04Z^NaHS04+ fHCl. 

As sodium chloride is much cheaper than hydrogen 
chloride, the hydrogen chloride is generated by the above 
reaction in the apparatus in the preparation of chlorine by 
the manganese dioxide method : — 

2NaCl + Mn02 + 2H2S04^Na2S04+MnS04+2H20 + Cl2. 

Hydrogen chloride has a specific gravity of 1.26. One 
liter of hydrogen chloride weighs 1.63 g. These figures 
are experimentally determined or may be derived from data 
already given. One liter of hydrogen weighs 0.0899 g. 
and one of chlorine, 3.167 g. The sum of these, 3.256 g., 
divided by 2, as two volumes of hydrogen chloride are 
obtained, gives 1.6284 + . It is not always easy to keep 
in mind a large variety of values, such as these figures (see 
table), and in fact often it is not necessary. By knowing a 
few values and applying one or two principles the figures for 
any gas may be quickly derived. For example, first, sup- 
pose we want the figure representing the specific gravity of, 
say, chlorine. We have learned that the specific gravity of 
hydrogen is 0.069 -[-, hence it is 14.4 times fighter than air. 
These facts must be remembered. As each molecule of 



62 GENERAL INORGANIC CHEMISTRY 

hydrogen contains two atoms, then any volume of air 
weighs 28.8 + times as much as a corresponding volume of 
free hydrogen atoms. As chlorine has two atoms in the 
molecule, the molecular weight is 35.45 x 2 = 70.9. If 
this is divided by 28.8 +, we get 2.45 as the value desired. 
Second, suppose we want the figure representing the weight 
of a liter oi a gas. The weight of a liter of air is 1.29 + g., 
the third fact to be remembered. The figure obtained by the 
first procedure, that is, the specific gravity, is multiplied by 
1.29; in this case, 2.45 x 1.29 = 3.16 g. for the weight of a 
liter of chlorine. These data presuppose a knowledge of 
the molecular weight. Third, in case we have a gas whose 
molecular zveigJit is unknown, we may derive it by experi- 
mentally determining the weight of a liter and reversing 
' the calculation. Divide that value by i .29 + and we secure 
the specific gravity, which, multiplied by 28.8 +, gives the 
molecular weight. For chlorine we secure the figure 70.76. 
As the atomic weight of chlorine is 35.45, we know the 
molecule contains two chlorine atoms. 

One part of water at + 15° dissolves 450 times its 
volume and at 0° 505 times its volume of hydrogen 
chloride, giving the concentrated acid. The dilute acid 
contains 10 per cent of hydrogen chloride. The solution 
is a strong acid which dissolves many metals, oxides, and 
carbonates. At — 22° crystals of HCl, 2 H2O separate out. 
At 110° a liquid containing 20.24 per cent distills over, 
which indicates some form of union between HCl and a 
definite amount of water, HCl, 8 H2O. 

Hydrogen Bromide, HBr, Hydrobromic Acid. 

Hydrogen and bromine also combine when heated to- 
gether. Hydrogen bromide is not prepared pure by the 
action of sulphuric acid on sodium bromide, as hydrogen 
chloride is obtained from sodium chloride, for the strong 



HALOGEN ACIDS 63 

sulphuric acid brings about decomposition with the pro- 
duction of free bromine. This is probably due to a weaker 
attraction between hydrogen and bromine than exists be- 
tween hydrogen and chlorine. 

It is prepared by using another and weaker acid, as 
phosphoric : — 

(a) 2NaBr + H3P04:±Na2HP04 + t2HBr, 

or more usually by the action of v/ater upon phosphorus 
tribromide : — 

PBrg + 3 H20i:^P(OH)3 + 1 3 HBr. 

In practice the bromide is made in the same apparatus. 
Then we have this reaction : — 

(^) P+3Br + 3H20:i^P(OH)3 + t3HBr. 

An 82 per cent solution may be had which has a specific 
gravity of 1.78. 

Hydrogen Iodide, HI, Hydriodic Acid. 

Hydrogen and iodine do not combine when brought 
together, except on careful and gentle heating. The re- 
action is endothermic. Such compounds are readily de- 
composed, as they are in unstable equilibrium. This one 
breaks up easily into hydrogen and iodine, and has the 
power of removing oxygen from other substances, as the 
hydrogen is liberated in the nascent state. It will be ob- 
served that the stability of these compounds decreases 
with the increase in molecular weight. 

Hydrogen iodide is prepared according to equation (^) 
given for hydrogen bromide, by substituting iodine for 
bromine. 

Hydrogen Fluoride, H2F2 or HF, Hydrofluoric Acid. 

While resembling the other halogen hydrides in many 
respects, hydrogen fluoride differs in several ways. The 



64 GENERAL INORGANIC CHEMISTRY 

pure compound is made by heating hydrogen potassium 
fluoride : — 

2HKF2Z?:2KF + tH<^F2. 

For ordinary purposes, however, calcium fluoride is treated 
with sulphuric acid. This preparation contains water from 
the acid used. 

CaF2 + H2S04:±CaS04 + f H2F2. 

It is a colorless liquid below + 19°. Above that it is a 
colorless gas with a very irritating odor. Below +40° it 
has the formula H2F2, whereas above + 88° it is HF. 

The utmost care must be exercised in handling this acid. 
A drop upon the hand, especially under the finger nail, 
produces a mean sore, sometimes requiring months to heal. 
It attacks many substances vigorously, especially when 
any silicon compound, as quartz, is present. When free 
from water, it does not attack these substances. The 
water solutions are kept in platinum, caoutchouc, or cere- 
sine vessels. It is used for etching glass. It is produced 
in large quantities, but dihited, in the manufacture of phos- 
phatic fertihzers. If it is allowed to escape freely in 
the air, serious injury to plants and animals is liable to 
result. 

Acids. These halogen compounds all admit of hydro- 
gen being readily replaced by more strongly electro- 
positive elements, as the metals. They are known as 
acids ; in this particular case, halogen acids. In acids 
the negative characteristic of the whole compound pre- 
dominates. Acids, as a rule, are sour when soluble. 
They change vegetable colors, and form salts. 



HALOGEN ACIDS 65 

HALOGEN ACIDS 



Name .... Hydrogen 


Hydrogen 


Hydrogen 


Hydrogen 


Fluoride 


Chloride 


Bromide 


Iodide 


Symbol . . . H,,F.; (above 


HCl 


HBr 


HI 


+ 88^ HF) 








Molecular weight 40 (or 20) 


36.46 


81 


128* 


Ordinary name in 








water solution . Hydrofluoric 


Hydrochloric 


: Hydrobromic Hydriodic 


acid 


(muriatic) acid acid 


acid 


Physical state . . gas (liquid 


gas 


gas 


gas 


below +19'') 








Specific gravity . 0.69 (below 


1.26 


2.79 


4.4 


+ i9'' = o.98) 








Boiling-point . . + 19° 


-83° 


-ys'' 


-34°t 


Melting-point. . -92.5° 


-116° 


-87° 


-51° 


Solubility in water 35.3% 


42% 


49% 


57% 


Specific gravity of 








solution . - .1.15 


1. 21 


1.49 


1.70 


Heat of formation 38.6 Cal. 


22 Cal. 


8.4 Cal. 


- 6 Cal. 


Dissociates at 


+ 1 500^ 


-f8oo° 


+ 180° 



* Round figures used. 

t Under four atmospheres pressure. 

EXERCISES 

1. Why was it necessary to prove that hydrogen chloride con- 
tained no oxygen ? 

2. How much salt is necessary to produce 480 g. of chlorine, 
and how much space would be filled by that amount of chlorine 
at 20° C. and 755 mm. pressure ? 

3. The specific gravity of hydrogen iodide is 4.4. Calculate 
its molecular weight. 



CHAPTER X 
THE ALKALI METALS 

Combined with the halogens in sea water are several 
metals, but two in particular, sodium and potassium, ap- 
propriately claim attention at this point. Compounds of 
these metals have been known and used since very early 
times. The Israelites used a mineral-alkali (natrona, — natu- 
ral sodium carbonate) for washing purposes. For a long 
time these caustic alkalies were regarded as undecompos- 
able. Just a century ago, Davy, by the use of the electric 
current, and Gay-Lussac and Thenard, by heating the 
caustic alkahes with iron fiHngs, obtained brilHantly lus- 
trous, crystalline metals which decompose water, re-form- 
ing the fixed caustic alkalies. 

Sodium is found in many silicates (oligoclase, NaAlSigOg, 
with some Ca, and labradorite, CaAlgSigOg, with some Na), 
sulphates, carbonates, borates, fluorides (cryolite), and so 
forth, but chiefly as sodium chloride, or common salt, in 
the sea and as rock salt. 

Potassium is a constituent of certain silicates, as mica 
and feldspar (orthoclase, potassium feldspar, KAlSigOg; 
albite, soda feldspar, NaAlSigOg), and occurs as salts, 
frequently accompanying sodium. It is found in the ashes 
of plants, of which it is a necessary constituent. Formerly 
most of it was obtained from wood ashes ; now it comes 
mainly from the Stassfurt salt beds of Germany. 

The year after Arfvedson discovered lithium, so named 
by Berzelius because he thought it was to be found only in 

66 



THE ALKALI METALS 6/ 

minerals, Gmelin (1818) observed that its salts gave a red 
coloration to an alcohol flame. Lithium is a constituent of 
some silicates (lithia mica), soils, plants (as tobacco and 
beet roots), and waters. It occurs very widely distributed, 
but in exceedingly small amounts. 

Rubidium constitutes 0.5 per cent of the mineral lepid- 
olite. It is present to the extent of 0.025 per cent 
in carnallite (KCl,MgCl2,6H20), one of the important 
Stassfurt salts. About 1,500,000 tons of potassium salts 
are mined at Stassfurt yearly. Some 300 tons of rubidium 
are annually distributed, mostly with fertilizers. Rubidium 
salts, which occur in saline waters, give two red and two 
violet lines in the spectrum, which are characteristic. 
. Caesium is found in the mineral pollucite (caesium alumi- 
num silicate), and was discovered in the mother liquors 
obtained by evaporating large quantities of saline water. 
Its salts give two characteristic lines in the blue portion of 
the spectrum. Caesium was the first metal to be discovered 
by means of the spectroscope, which instrument has made 
our knowledge of this and other worlds vastly broader. 

These five metals may be prepared : — 

Fh'st, by passing a direct electric current through the 
fused compounds, as NaOH. 

Second, by electrolysis of a haHde in a proper liquid, as 
pyridine, in this particular case : — 

2\AQ\-:±2 Li+tCl2. 

Third, by heating a carbonate with carbon or iron 
carbide : — 

K2C03 + 2C:^2K + t3 CO. 

All have a bright, lustrous, metallic appearance when 
freshly cut; all are soft and have low melting-points. 



6S GENERAL INORGANIC CHEMISTRY 

Lithium is the Ughtest of all the elements that are solid at 
the ordinary temperature. It floats upon naphtha. 

They are all intensely electro-positive and hence have 
powerful attraction for electro-negative elements, like 
oxygen and the halogens. They decompose water at 
ordinary temperatures, evolving hydrogen and forming 
hydroxides : — 

2 Na + 2 H20:i^2 NaOH + fHa; 

hence, they must be kept in petroleum or one of its 
products. In decomposing water by means of potassium, 
the hydrogen takes fire at once, the flame having a purple 
color. Sodium must be confined to take fire. It gives a 
yellow color to the flame. 

They form alloys with certain metals, as lead, giving 
**hydrone," which reacts with water as above. The lead 
serves as a convenient medium for diluting the sodium and 
a safer means for its transportation. They form amalgams 
with mercury, being dissolved by the quicksilver. 

The hydroxides formed by the action of the alkali 
metals on water are all soluble in water and cause lituius 
to assume a blue color. They are known as i?ases. If we 
write the formula for water in this manner, H — OH, 
and the formulas of the hydroxides underneath, Li — OH 
it appears that a base may be defined as water Na — OH 
in which one hydrogen atom has been replaced K — OH 
by an electro-positive element. It will be ob- Rb — OH 
served that two elements (OH) persist in these Cs — OH 
compounds together. They constitute an electro-negative 
group, as it were. It is known as Jiydroxyl and is pres- 
ent in a large number of compounds. There are insoluble 
bases known. Those soluble in water as a rule change 
vegetable colors. 



THE ALKALI METALS 



69 



PROPERTIES OF THE ALKALI METALS 



Name . . . 


. Lithium 


: Sodium 


Potassium 


Rubidium 


CESIUM 


Derivation . 


(stone) 


(natrium) 

soda 
(natrona) 


(kalium) 
potash 
(alkali) 


rubidus 
(dark red) 


csesius 
(blue-gray) 


Symbol . 


Li 


Na 


K 


Rb 


Cs 


Discoverer . 


. Arfved- 


Duhamel 


Duhamel 


Bunsen 


Bunsen 




son 


du Mon- 


du Mon- 


and 


and 






ceau and 


ceau and 


KirchhofF 


Kirchhoff 






Marggraf 


Marggraf 






Date . . . . 


1817 


1732 and 
1759* 


1732 and 
1759* 


1 861 


i860 


Atomic weight . 


7.00 


23.00 


39.10 


8545 


132.81 


Specific gravity 


0.59 


0.98 


0.87 


1.52 


1.85 


Melting-point . 


+ 180 = 


+ 95.6° 


+ 62° 


+ 38.5° 


+ 26.5° 


Boiling-point . 


>95o- 


+ 742^ 


+ 667^ 


.... 


4- 270° 


Alcohol flame 












colored . 


red 


yellow gray-purple 


dark red 


blue-gray 



If we again write the formula for water, H — OH, 
and the formulas of the halogen acids beneath, H — CI 
we get — H — Br 

H-I 
Therefore it appears that an acid is water in which the 
hydroxy} has been replaced by an electro-negative element. 
We know of no acid without a replaceable hydrogen atom. 

If we bring an acid and a base together, 

NaOH + HCl->H20 + NaCl, 

water is eliminated and a salt'i^ produced. Neutralization 
has taken place. We determine the neutral point by adding 



* Compounds of these metals have been known since ancient times. The 
sava7its named first showed the distinction between soda-ash and pot-ashes. 
In 1807, Humphry Davy first obtained the elements by electrolyzing the 
fused alkalies. 



70 GENERAL INORGANIC CHEMISTRY 

a few drops of a litmus solution. The acid turns this red, the 
base blue. At the point when just a drop of either solu- 
tion of acid or base causes the liquid to assume one color 
or the other, it is said to be neutralized. Elaboration of 
these terms will become necessary later, but what is given 
above will answer our present requirements. 

Application of the principle of neutralization gives us a 
means for quantitative analysis, for a definite amount of 
a base requires a definite amount of acid to neutralize it. 
If we have 2 g. of NaOH, for example, dissolved in water, 
we need 1.825 g- HCl with which to neutralize it. This 
figure is derived from the molecular proportions : — 

NaOH:HCl 

40 : 36.5 \\2\x= 1.825. 

The amount of water present as the solvent is imma- 
terial as far as the reaction is concerned, but of importance 
in determining the strengths of the solutions involved. 
For instance, the 1.825 g. HCl may be in 100 or 1000 cc. 
By dividing the weight of the solute by the volume of the 
solvent we get the strength. In this manner we are able 
to determine the strength of an unknown solution. Once 
the strength of a solution becomes known, it becomes a 
standard sohttion. If the solution contains in 1000 cc. the 
number of grams equal to the molecular weight of the 
solute, it is called a molar solution. For example, 40 g. of 
NaOH and 36.5 g. HCl each in 1000 cc. are molar solu- 
tions. One cubic centimeter of one such solution neutral- 
izes I cc. of the other. Another term, normal solution, 
is also applied to such solutions, but it does not always 
mean the same thing. Sulphuric acid (HgSO^), for in- 
stance, has two hydrogen atoms, which may be replaced 



THE ALKALI METALS ■ 71 

by a metal; therefore, it has a double equivalence. Normal 
solutions refer to this equivalence. 

A molar solution of sulphuric acid contains 98 g. to the 
liter (2 + 32 4- 64 = 98), whereas the normal solution con- 
tains one half (49 g.) that amount. In the case of the 
HCl, the normal and the molar solutions are the same. 
A standard solution containing one half, one tenth, or 
other fraction (x) of a normal or molar strength is indi- 

N N N M M M 
cated by symbols in this manner: — , — , — , or — , — , —, and 
^■^ 2lO;r 2lO;i' 

so forth. A multiple molar or normal solution is indi- 
cated by the integer being placed in front, as, 2 M, 5 M, or 
3 N, 5 N, and so forth. 

The use of solutions in analysis in this manner is known 
technically as acidinietry or alkalimetry. 

EXERCISES 

1. Compare the specific gravities, melting and boiling points, 
of the alkah metals, and see if any relationship appears with the 
atomic weights. 

2. Explain the relationship of an acid, a base, and a salt. 

3. How much of the following substances are in their molar so- 
lutions : hydrogen bromide, potassium hydroxide (KOH), and 
potassium iodide (KI) ? 

4. Suppose we have a molar solution of sodium hydroxide and 
a hydrogen chloride solution of unknown strength. If 50 cc. of 
the former require 62 cc. of the latter for neutralization, what is 
the strength of the hydrochloric acid solution? 



CHAPTER XI 

NITROGEN— AMMONIA — LIQUEFACTION OF GASES — 
COMPOUND RADICALS 

Nitrogen, N. At. Wt, 14.01. M. Wt, 28.02, Ng 

In 1772 Rutherford discovered that part of the air did 
not support respiration or allow combustion. It was called 
*' mephitic " or '' phlogisticated air." Lavoisier called it 
azote (devoid of life). Chaptal gave it the English name 
nitrogen, indicating a producer of niter or saltpeter (KNO3). 

In the free state it constitutes four fifths by volume or 
three fourths by weight of the air. It is combined with 
oxygen in nitric acid and in the nitrates ; with hydrogen in 
ammonia and its compounds. Nitrogen is an invariable 
constituent of protoplasm and many animal and vegetable 
substances. No living matter is known free from nitrogen 
compounds. 

It is prepared, but in an impure form, by the removal 
of oxygen from the air ; either 

(^) By burning phosphorus in the air ; or, 

(^) By the absorption of the oxygen of the air by an 
alkaline pyrogallate. 

It is prepared pure by heating ammonium nitrite: 

NH4N02->2H20+ JN2. 

It is a colorless, odorless, tasteless gas, with sp. gr. o 97, 
b.-p. — 193°, freezing-point — 203°. The specific gravity of 
the sohd at — 214° is 0.885. One liter weighs 1.2507 g. 
Water dissolves 0.015 volume at ordinary temperatures. 

Nitrogen is a very inert element, combining directly 

72 



NITROGEN ■ 73 

only with lithium at ordinary temperatures (LigN), and a 
few other metals, as magnesium (Mg3N2), when heated. 
Under the influence of sparks from high-tension electric 
currents it combines with oxygen. Indirectly it combines 
with many of the elements, giving important ammonium 
and nitric acid compounds, explosives, alkaloids, and al- 
bumenoid substances. Decay usually starts in the last- 
mentioned compounds of nitrogen. It is not itself a 
poisonous element, but many of its compounds are. 

It serves not only to dilute the oxygen of the air, and 
thus prevent combustion processes once inaugurated from 
bringing about a rapid destruction of our living world, but 
is an essential constituent of plant food. Free nitrogen 
is not a direct food for vegetation. It must be in the form 
of compounds like ammonia, or nitrates, or the many com- 
plicated compounds we find produced in the growth and 
decay of living things. There are certain plants, like 
peas, beans, clover, and so forth {legiiminosce), which have 
nodules upon their roots. These nodules contain bacteria 
which have the power of converting free nitrogen into com- 
pounds, chiefly albumins. These bodies are digested and 
absorbed by the roots of the plant. Some of the nodules 
often contain as much as 5 per cent of combined nitrogen. 
The roots of such plants are not harvested, but are 
plowed into the soil, thus enriching it. Nitrogen com- 
pounds that are usually applied as fertilizers, are soluble 
in water, or readily undergo decomposition (nitrification 
and denitrification), forming the soluble compounds, hence 
are washed out of the soil. Nitrogen is therefore the 
most expensive of the essential elements for plant growth. 
The discovery of the ability of the leguminosae to utilize 
the free and abundant nitrogen of the air constituted one 
of the greatest contributions to agronomy. 



74 GENERAL INORGANIC CHEMISTRY 

Ammonia, NHg. M. Wt, 17.03 

Of the compounds of nitrogen and hydrogen we need 
give attention here to but one, namely, ammonia, which 
was called " alkaline air " by Priestley, who discovered it 
(in 1774). In 1785 Berthollet proved its composition. 

It occurs in very small amounts in the air and rain in 
compounds, as the carbonates, nitrates, and nitrites. It 
results from the decay of nitrogenous organic matter (de- 
nitrification). Ammoniacal salts are found in plant and 
animal matter, especially in decomposed urine. 

Four processes for the preparation of ammonia may be 
considered, as they separately illustrate principles: — 

1. Nitrogen and hydrogen can be made to combine 
under the influence of a silent electric discharge : 

N,+ 3H2^2NH3; 

but the yield is small. It is a reversible reaction. 

2. Decomposition of a metallic nitride with water : 

MggN^ + 3 H^O -^ 3 MgO + \ 2 NH3. 

3. Decomposition of a compound of ammonia itself : 
{a) by heating ammonium hydroxide, 

NH^OHl^f NH3 + H2O; 

{h) by contact, or heat, with a metallic oxide (calcium 
oxide), 

2 NH4Cl + CaO^Caa2 + H20+ f 2 NH3. 

4. By breaking up compHcated compounds of nitrogen 
by heat; for instance, when wood, coal, animal refuse, and 
so forth, are heated in a retort, so arranged that the oxygen 
of the air is excluded. This is known as the process of 
destructive distillation, which is extensively used commer- 



LIQUEFACTION OF GASES 75 

cially and is so complicated that no chemical equations 
have been devised to show exactly what takes place. 

Ammonia is a colorless gas with a very pungent odor, 
familiarly known in smelhng salts. .It is lighter than air 
(sp. gr. 0.59). Under a pressure of 6.5 atmospheres, or 
when cooled to — 40° under ordinary pressure, it con- 
denses to a colorless, mobile liquid (sp. gr. 0.623), which 
freezes at —85°. Its melting-point is — 75°' and boiling 
point -34°. 

Liquefaction of Gases. Boyle, Northmore, van Marum, 
Faraday, and others, found many gases could be converted 
into Hquids on increase of pressure, especially if the gas 
was simultaneously cooled. Up to 1877 hydrogen and sev- 
eral other gases were considered non-condensable, although 
Natterer (1852) had apphed a pressure of over 3000 at- 
mospheres. In 1869 Andrews discovered a principle, the 
ignorance of which caused previous failures ; namely, that 
each gas has a temperature above which no amount of 
pressure so far attainable suffices to condense it to a liquid. 
This is known as the critical temperature^ and the pressure 
exerted by the particular gas at that temperature is known 
as the critical pressure. Since the acquisition of this 
knowledge, all gases have been converted into Hquids, and 
many into solids. 

Cullen observed that when a liquid was rapidly con- 
verted into a gas, cold was produced. This principle has 
been applied in making ice machines. If ammonia gas 
is compressed, it changes into a liquid. The heat liber- 
ated is removed by cold water flowing through pipes im- 
mersed in the hquid. The cooled Hquid ammonia, when 
run into other pipes under less pressure, evaporates and 
absorbs heat from any surrounding liquid, which is usually 
one not frozen, or only partially frozen, at the low tern- 



"J^ GENERAL INORGANIC CHEMISTRY 

perature produced. This very cold liquid, usually a calcium 
chloride brine, is led by pipes through the localities to be 
cooled back to the refrigerating machine, where it is again 
chilled. The ammonia gas flows out through a separate sys- 
tem of pipes, is recondensed, and used over again. The 
brine and ammonia are in separate closed systems of pipes. 

Pure liquid ammonia does not conduct a current of elec- 
tricity. It dissolves many solids and, like water, forms 
crystalline compounds (ammonia of crystallization), am- 
moniates, similar to the hydrates. 

Ammonia is exceedingly soluble in water ; at + i6° water 
dissolves 739 and at 0° 1148 times its volume. It cannot, 
therefore, be collected over water, but may be over mer- 
cury or by upward displacement. The water solution is 
known as ammonium hydroxide, aqua ammonia, or spirits 
of hartshorn. The concentrated solution at -f 15° contains 
35 per cent and has a specific gravity of 0.882. When am- 
monium hydroxide is heated, ammonia is driven off. Care 
should be exercised in opening a fresh bottle of ammonium 
hydroxide, especially in warm weather, as the contents are 
often charged at low temperatures. 

Ammonia is not ordinarily considered a supporter of 
combustion. It burns when the gas is held in a flame, 
but ceases to burn when not heated. It burns in oxygen, 
however. 

Compound Radicals. Ammonia acts like an element in 
many ways. It is decomposed, however, when passed over 
certain heated metals : — 

2NH3 + 2K-^2NH2K4-H2. 

Ammonia combines directly with hydrogen chloride to 
form ammonium chloride : — 

NH, + HC1 = NHXI 



COMPOUND RADICALS 7/ 

The formula for ammonium hydroxide is written NH^OH. 
The (NH4) group enters many compounds in the same 
manner as an element (NaCl, KCl, NH^Cl), and forms 
an amalgam as sodium does, although free ammonium 
has not been prepared. When a combination of atoms 
acts like an element, we speak of the combination as a 
compound radical. 

Ammonium hydroxide turns litmus paper blue, neutral- 
izes acids, and acts like sodium hydroxide, except that in 
gentle heat it is decomposed, with the evolution of ammonia 
gas. We readily appreciate why Priestley designated it 
*' alkaline air." 

We may now enlarge our definition of a base. — 
A base may be regarded as water (H — OH) in which 
one hydrogen atom has been replaced by an electro-positive 
element or compound radical {^'d.OW, KOH, NH^OH). 

EXERCISES 

1. How much nitrogen may be obtained from 22 g. of ammo- 
nium nitrite? What volume would it occupy at + 20° and 756 
mm. pressure? 

2. What are the principles illustrated in the methods given for 
the preparation of ammonia ? 

3. What relation is there between the principles involved in the 
liquefaction of gases and vapor tension ? 

4. Why should care be exercised in opening vessels containing 
concentrated ammonia water? 



CHAPTER XII 
THE AIR AND ITS CONSTITUENTS — THE NOBLE GASES 

About the ninth century chemists knew that metals were 
altered when calcined in the air. Jean Rey proved the 
materiality of air, which was confirmed by Galileo in 1640 
and von Guericke, by means of the air pump, in 1648. In 
the seventeenth century Hooke suspected that the air con- 
tained the gas given off by heating niter. Mayow, in 1669, 
demonstrated that the volume of air contained in a vessel 
over water was diminished by respiration as well as by 
combustion. Becher, in 1700, thought combustion origi- 
nated from a peculiar volatile substance escaping from the 
earth or a kind of sulphur. Stahl, his pupil, in 1720, put 
forward the hypothesis of " phlogiston," or " burnableness," 
which he said was the substance that escaped in combus- 
tion. Rutherford, in 1772, discovered nitrogen, and Bayen, 
in 1774, showed that mercuric oxide was reduced without the 
addition of phlogiston. These led Lavoisier to his experi- 
ments on the absorption of air by the calcination of metals 
and to his demonstration of the law of the conservation of 
matter. A century later Rayleigh and Ramsay proved 
the presence of argon. 

The exact thickness of the gas envelope surrounding the 
earth, called the atmosphere, is not known. It is essen- 
tially a mixture of nitrogen, oxygen, and argon (including 
the so-called ** noble gases "), with a certain more or less 
constant admixture of carbon dioxide and variable amounts 
of aqueous vapor and oxygen, nitrogen and hydrogen com- 

78 



THE AIR AND ITS CONSTITUENTS 79 

pounds. There are also found fortuitous substances, like 
dust, sulphur dioxide, and so forth, depending upon the 
locality, time, and conditions. 

The air is not constant in its com.position. Certain con- 
stituents vary but slightly, however, from a definite percent- 
age. The air over the sea, upon mountain tops, in deep 
mines, and in cities appears to be different, and does differ 
in detail, but the average analysis of samples of air col- 
lected the world over, eliminating all but the first three 
constituents mentioned, shows the following composition : — 

Per Cent Per Cent 
by Volume by Weight 

Nitrogen 78.06 75.5 

Oxygen ' 21.00 23.2 

Argon 0.94 1.3 

In making the analysis a definite volume of air is first 
treated with yellow phosphorus in wire form. This quickly 
combines with the oxygen, the amount of which is deter- 
mined by the shrinkage in volume. The remaining gas is 
then passed over heated magnesium, which combines with 
the nitrogen (Mg3N2). That which is not removed is argon. 

The air is not a compound, because (i) the constituents 
are not present in atomic proportions ; (2) when the ele- 
ments composing air are mixed to form air, there is neither 
an absorption nor an evolution of heat, which would indi- 
cate chemical combination ; and (3) the constituents of the 
air vary in their solubihty in water. Air, expelled from 
water, contains 34.9 per cent of oxygen and 65.1 per cent 
of nitrogen. 

One liter of air weighs 1.29276 g. Air is 773 times 
lighter than water. It is 14.39 times heavier than hydrogen. 
By application of the principles governing the liquefaction 
of gases, namely, with slight pressure and intense cooling, 



8o GENERAL INORGANIC CHEMISTRY 

it is converted into a colorless liquid (Processes of Hamp- 
son and Linde), with boiling-point — 190°, specific gravity 
0.995. It is usually turbid, due to the presence of solid 
carbon dioxide in suspension. Nitrogen boils at — 193° 
and oxygen at —184°; consequently, after standing, much 
of the nitrogen boils off, and the liquid air contains about 
54 per cent of oxygen instead of 23 per cent. With care 
the percentage of oxygen may be increased to 90 or even 
95. By its evaporation, great cold is produced. The 
properties of many substances are altered by this intense 
cold. Rubber loses its elasticity and becomes hard and 
brittle. Flowers dipped into liquid air are easily shattered 
into minute fragments by the least pressure. Chemical 
reactions are especially slow, some violent ones scarcely 
proceeding at the temperature of —193°. Experiments 
with liquid air on a large scale and modern cryogenic in- 
vestigations were made possible by the use of glass vessels 
of double walls separated by a vacuum. Dewar perfected 
these by silvering the walls of the evacuated space to re- 
duce the heating effect of transmitted light. 



THE NOBLE GASES 

In 1892 Rayleigh noted that while a liter of nitrogen 
obtained from the air weighed 1.257 1 g-j a- liter of the pure 
gas weighed 1.2507 g. He and Ramsay then separated 
from the air a new element, called argon, by the method 
given above. It received its name on account of its chemi- 
cal inactivity. We inhale about 20 1. of this gas every day. 
As far as we are aware, it is devoid of physiological action. 
One hundred volumes of water dissolve 4 volumes of argon 
at +12°; hence it is found in rain-water. Argon is 
therefore present in many waters, and the gases from 



THE NOBLE GASES 



8i 



springs, as well as in certain minerals like cleveite, uraninite, 
and malacone. It has been found in meteorites, and the 
gases contained in rock salt. It boils at — 185°, and forms 
ice-like crystals at — 189.5°. 

In 1868 Jannsen and Lockyer observed lines in the chro- 
mosphere of the sun which could not be attributed to any 
known chemical element, and helium was prognosticated. 
In looking for richer sources of argon, Ramsay found these 
lines in gases obtained from certain minerals. It is a very 
inert gas. One hundred volumes of water at +18° dis- 
solve 0.73 volume of helium. This gas resisted liquefac- 
tion longer than any other. As these pages pass through 
the press, Onnes, in Leyden, announces that he has hque- 
fied it, and that it boils at — 268.5°. Ramsay and Travers, 
after fractioning large quantities of liquid air, also separated 
out neon, krypton, and xenon. These occur in extremely 
small amounts in the air. 





Derivation of Names 


Atomic Weight 


One Part by Volume 
in Air 


Helium — :^Xtos — sun 




4.0 


2,450 vols. 


Neon — v£os — new 




20. 


808 vols. 


Argon — apyo? — idle 




39 9 


105 vols. 


Krypton — k/ovttto? — cone 


ealed 


81.8 


746,000 vols. 


Xenon — ^evos — stranger 




128.0 


3.846,000 vols. 



The experimental difficulties attendant on investigations 
at such low temperatures as were necessary in the discovery 
and study of these gases, were very great. We can picture 
the difficulties to be encountered in working with ordinary 
substances, if all the apparatus is at the temperature of 
boiling oil of vitriol ( -f 270°). These difficulties were sur- 
mounted by the experimental ingenuity of Dewar, Ramsay, 



82 GENERAL INORGANIC CHEMISTRY 

Olszewski, and Onnes, for ordinary zero is that much 
higher than the lowest temperature so far attained. 

These gases have one atom in the molecule (monatomic). 
They are more inert than nitrogen. No compounds have 
been prepared which give evidence of the union of any of 
these five elements with other elements or even with each 
other. They are therefore called "noble gases." Under 
certain conditions different ones are obtained from radio- 
active compounds (Chapter XXV). 

Carbon dioxide (CO2) is a constant constituent of 
the air, averaging about 3.5 parts per 10,000. On high 
mountains the figure falls to 2 parts, while it is much 
higher at other places. Inspired air containing 3 parts is 
expired with 400 parts of carbon dioxide per 10,000. The 
percentage of oxygen drops from 21 to 17, or lower. An 
inhabited room with ordinary ventilation contains 6 to 7, and 
with poor ventilation 30 and more parts of carbon dioxide 
per 10,000. 

The carbon dioxide in the air comes mainly from the 
oxidation of organic matter (vegetable, animal, and mineral), 
either by combustion, or respiration, or from decomposition. 
Estimating the population of the globe at one and a half 
billions, mankind alone exhales one and a half million tons 
of carbon dioxide every day. In the city of New York 
about 100,000 tons of carbon dioxide are daily poured into 
the air from the combustion of fuel. We have an uninter- 
rupted and constant production of carbon dioxide through 
the decay of vegetable matter. Large quantities come 
from mineral springs and volcanoes. Carbon dioxide is 
heavier than the air and accumulates in some low places, 
as wells, fermenting rooms of breweries, and some valleys. 
Through the agency of the winds, rains, and the ceaseless 
movement of the molecules (diffusion), it is distributed in 



THE NOBLE GASES 83 

the atmosphere. This is very fortunate. A candle ceases 
to burn when the percentage of oxygen gets below 18. 
To avoid danger from vitiation of the air, it has become 
generally recognized that from 16 Jto 20 cubic meters of 
air are required per individual per hour. In the best 
ventilated hospitals about 100 cubic meters are provided. 
Under normal conditions of health half that amount is 
sufficient. As a general rule, the atmosphere of a room 
may be considered vitiated as soon as it begins to " smell 
close." This condition is not all due to carbon dioxide, 
however, but to organic substances, only partly known, 
which are exhaled by man and animals, probably as much 
from the skin as from the lungs. We have no simple 
method for estimating these organic substances. They may 
be regarded as roughly proportional to the carbon dioxide, 
so a safe criterion in judging the quality of the air is the 
determination of the amount of carbon dioxide present. 
This may easily be done by its conduct with clear lime- 
water, which, on coming into contact with carbon dioxide, 
becomes turbid : — 

Ca(0H).3 4- CO.2 -^ I CaCOg* + H^O. 

Aqueous vapor is always present. Its quantity depends 
upon the temperature and corresponds to the vapor tension 
of water. One cubic meter of air saturated can contain 
22.5 g. of water at + 25°. On cooUng to 0°, 17. i g. separate 
out. It has been estimated that there are 72 x 10^^ tons of 
water in the air. Aqueous vapor is very unequally diffused. 
Generally air contains from 50 to 70 per cent of the 
quantity of vapor necessary for complete saturation. The 
amount of vapor in the air may remain the same, while 
the temperature varies and it feels "too dry" or "too 

* The arrow pointing down indicates formation of a precipitate. 



84 GENERAL INORGANIC CHEMISTRY 

wet." The air, when dry, irritates the respiratory organs ; 
when too moist, it impedes transpiration and its beneficent 
effects. The total amount of water present, therefore, plays 
a less important part than its relation to the temperature. 

The other constant constituents in the air, but in very 
variable amounts, are ozone, hydrogen dioxide, and nitrogen 
compounds, as ammonium carbonate, nitrite, and nitrate. 
They are supposed to be produced through electrical and 
light influences, and are swept to the ground by the 
precipitation of aqueous vapor. 

There are many incidental impurities in the air that are 
local and more or less evanescent. In the combustion of 
coal, sulphur is burned to sulphur dioxide. In the city of 
New York over a thousand tons of sulphuric acid from 
this source are poured into the air every day. The city 
of Manchester, England, looks Hke a forest of chimneys, 
the black smoke (soot) constituting the foliage. Finely 
divided particles of solids (soot, clay, sand, refuse of all 
kinds, and so forth) are whipped up by the winds to give 
us dust. Aside from general objections to personal discom- 
fort from flying particles of solid material, whatever be its 
nature, there is a specific one. These particles are the 
bearers of germs, many of which are pathogenic. When 
these germs come into contact with material suitable for 
food and conditions favorable to growth, they develop with 
tremendous rapidity. Processes of fermentation, decay, and 
disease are thus inaugurated. Air free from sohd particles 
is free from bacteria. We may rid the air of them by passing 
it through 30 to 40 cm. of cotton. 



THE NOBLE GASES 85 



EXERCISES 

1. What is the principle underlying the construction and use 
of Dewar flasks ? 

2. How many cubic feet of air are taken into the lungs (average) 
every hour, and how many cubic feet should be supplied per person 
in a well-ventilated room ? 

3. How would you account for the fair degree of uniformity in 
the niixture of gases constituting the air? 

4. Why do we say air is a mixture? 

5. From the following data calculate the weight in kilograms 
of each constituent of the air in a room 12' x 15' X 9'. Assume 
water vapor 0.90 per cent, and carbon dioxide 0.03 per cent. 



CHAPTER XIII 
CARBON 

At. Wt., 12 

The element carbon and its compounds constitute the 
backbone of living things. It occurs in nature as : — ■ 

I. Diamond, in alluvial rocks of volcanic origin in India, 
Borneo, Brazil, and South Africa and^ in certain meteoric 
stones. It crystallizes in the regular system, mostly rhom- 
bic dodecahedra, occasionally as octahedra. It may be 
colorless, transparent, black, or varicolored, depending 
upon the impurities present. When diamonds are found, 
they are covered, as a rule, with a crust and possess none 
of the brilliancy we ordinarily associate with them. Pure 
diamonds have high dispersive and refractive powers for 
light. The best diamonds are the hardest known sub- 
stances. Some are softer than others, and have a grained 
structure, which is observed in the cutting. On account of 
the hardness, the black, impure form, bort, is used extensively 
in diamond drills for cutting and boring. The better grade 
is cut and polished into shapes, which must not be mis- 
taken for the underlying crystalline form, to produce the 
greatest luster and brilliancy, and used for gems. Dia- 
monds are sold by the " carat," equal to 3^ Troy grains or 
205 miUigrams. One of the largest diamonds ever found, 
the Ctillinan, weighed 621 grams, or about 3025 carats. 

The diamond has a specific gravity of 3.5 and is the dens- 
est form of carbon. It softens under intense heat ( -1-2500°), 
changing into the graphitic form of carbon. When heated 

86 



CARBON Sy 

to + 800° in the presence of oxygen, it burns to COg (in 
1694 by Averami and Targioni). The diamond is one of 
the most insoluble substances known. Carbon in general 
is very insoluble, but it does dis.solve in some molten 
metals, as iron and melted olivine (magnesium silicate), 
from which it may be crystallized on cooling under great 
pressure. Moissan prepared small synthetic * diamonds 
by the former process. He dissolved pure sugar charcoal 
in molten pure iron and suddenly cooled the very hot mass 
by plunging it into water. A hard exterior was thus pro- 
duced. As the interior, which remained liquid, solidified, 
the iron carbide (FcgC) crystallized with expansion and con- 
sequent production of great pressure upon any uncombined 
carbon within the iron ball. On dissolving the iron after- 
wards in acids, tiny crystals of diamionds were found. Car- 
bon, and a few other substances, on being heated, change 
into vapor before reaching the boiling-point. The critical 
temperature of carbon is +5800°. Its critical pressure is 
17 atmospheres. By exploding some of the very high 
explosives in steel bombs, strong enough to withstand 
enormous pressures, carbon has been had in the liquid 
form, and as it cooled, diamonds were produced (Abel, 
Noble, Crookes). In no cases have diamonds so far been 
produced synthetically of commercial size or in quantity. 
Greek writers mentioned diamonds 300 B.C. 

2. GrapJiite was known to the ancients, but was not distin- 
guished until 1565 (Gesner). It occurs as an amorphous, 

* To synthesize an element seems a contradictory term. In this case it is 
not. We know diamond is the densest form of carbon, and we have reason 
to believe it has the largest number of atoms in the molecule of any form of 
carbon. Therefore the term means an increase or building up of a larger, 
heavier, or more complex molecule. " Artificial " diamonds are made of glass 
and contain no carbon and do not possess the properties of diamonds, while 
" synthetic " diamonds do. 



88 GENERAL INORGANIC CHEiMISTRY 

grayish black, glistening, soft mass and as rhombic prisms 
and hexagonal plates in old rock formations in Siberia, 
Ceylon, and the United States. It is frequently called 
plumbago, or black lead, and is used in making lead 
pencils and stove poHsh. It has a specific gravity of 2.25. 
It is a good conductor of heat and electricity, hence is exten- 
sively used in making crucibles, in electroplating, and as elec- 
trodes, where heavy currents are used and substances like 
chlorine, sodium, phosphorus, or the alkaline hydroxides, 
which attack metalHc electrodes, are produced. It is 
attacked by some powerful oxidizing agents. It may be 
burned by heating in oxygen, but this occurs at a higher 
temperature than the diamond requires. It appears to be 
the stable variety of carbon, as other forms of carbon when 
heated pass into it. This is accomplished by fusing other 
forms of carbon with iron, but it is produced commercially 
in large quantities by heating carbon to a high tempera- 
ture, but below +4000°, by means of an alternating elec- 
tric current. It has an " oily feel " and is used as a 
lubricant where an oil would be decomposed by the heat 
or squeezed out by the weight of the machinery. Recently 
Acheson has also prepared graphite in such a fine state of 
subdivision that it remains suspended in water for months 
and readily passes through filters. 

3. AmorpJioiLS carbon is a term applied to a class to 
which belong the various grades of mummified and car- 
bonized remnants of ancient flora. They vary in their 
purity and have an average specific gravity of 1.5. The 
natural varieties are peat, lignite, bituminous and anthra- 
cite coal. The artificial varieties are coke, charcoal, gas- 
carbon, soot, lampblack, and animal charcoal. 

Each of these has specific properties and uses. All of 
the former and the first two of the latter group are used 



CARBON 89 

for fuel purposes and in metallurgical processes to reduce 
oxides to the metallic condition and to produce carbides. 
They contain ash, varying in percentage from i to 80. 
Charcoal absorbs many times its volume of various gases, 
for which reason it is often used for deodorizing and disin- 
fecting. When cooled by liquid air or hydrogen, this 
capacity is so increased that a vessel containing a gas 
may be brought to such a low vacuum as to prevent the 
passage of high-tension currents of electricity. Animal 
charcoal, containing about 75 per cent of bone ash, further- 
more absorbs coloring matter from many liquids, so is 
used in decolorizing sugar solutions before the white 
product is crystallized out. Coke and charcoal, common 
and animal, are made by the destructive distillation of coal, 
wood, and animal refuse, respectively. Gas carbon is pro- 
duced with the first and is used in electrical work. Soot 
and lampblack are produced by the incomplete combus- 
tion of carbonaceous material. They are virtually the 
same, and are used in making black printer's ink and 
paint. 

In 1773 Lavoisier showed the similar chemical nature 
of the allotropic forms of carbon. The purest carbon is 
made in the laboratory by charring sugar. 

Carbon occurs combined as carbon dioxide (CO2) in the 
air ; in carbonates, as limestone (CaCOg) and magnesite 
(MgCOg); as compounds with hydrogen in natural gas 
(methane, CH4),petroleum(heptane, CyH^g, benzene, CgHg), 
and asphalt; it is present, combined with other elements, in 
all animal and vegetable matter. 

Carbon does not readily form combinations with the 
metallic elements except at comparatively high tempera- 
tures, when it acts as a negative element. Many of these 
carbides are decomposed at +2500°. At ordinary tern- 



90 GENERAL INORGANIC CHEMISTRY 

peratures, it does not combine with oxygen, but when 
heated it forms two oxides, CO and CO2, with the produc- 
tion of considerable heat. It combines when red hot with 
sulphur to form carbon disulphide (CS2). 

EXERCISES 

1. How much carbon would be necessary to reduce 9 g. of 
copper oxide (CuO)? 

2. What principles underhe the production of diamonds from 
pure charcoal? 

3. How much carbon dioxide and disulphide, respectively, can 
be produced from 4 lb. of pure charcoal? 



CHAPTER XIV 
CARBON HYDRIDES — FLAME — ILLUMINANTS 

Although carbon combines directly with great reluc- 
tance, yet it forms a number of compounds, with hydro- 
gen. Many of these hydrocarbons occur in natural gas 
and petroleum ; many are made artificially, as in the destruc- 
tive distillation of wood and coal. Their study is extensive, 
and forms a prominent part of one of the divisions of 
chemistry called Organic Chemistry. For our purposes, 
we need consider only two of the hydrocarbons at present. 

Methane, CH^, m. wt. 16.032, was discovered by Volta 
in 1778. 

Methane occurs as '* marsh gas," where vegetable matter 
undergoes slow decomposition with hmited amount of oxy- 
gen present, as when organic matter decays beneath water. 
It occurs, also, as ''fire damp" in coal mines. It is the 
principal constituent of natural gas drawn from deep bor- 
ings in the earth, and is found in putrefactive gases expelled 
from the animal body. 

It may be prepared (i) by decomposing a carbide (alu- 
minum carbide) with water or acids : 

C3AI, -f 12 H20=^|4 A1(0H)3 -F t 3 CH4; 

(2) by decomposing a more complicated compound of 
carbon (sodium acetate) by heating with a solid caustic 
alkali : 

NaC2H302 + NaOH -± ^2.^C0^ + f CH^, 

It is a colorless gas, with a faint odor, slightly soluble in 

91 



92 GENERAL INORGANIC CHEMISTRY 

cold water; sp. gr. 0.56; b.-p. — 164°; m.-p. — 186°. It 
burns with a very hot, shghtly luminous flame : 

CH4 + 2 02^C02 + 2 H2O. 

It forms explosive mixtures with oxygen or the air. The 
explosion of such a mixture is the cause of most disasters 
in collieries. A mixture of fine coal dust and air is also 
explosive. The presence of dust, even if it is non-combus- 
tible, renders the effects of the explosion more disastrous. 
Many miners who do not suffer greatly from the shock of 
the explosion are subsequently killed by the *' after damp," 
which is a mixture of the oxides of carbon. 

CH4 is neither acidic nor basic in character. It may 
give up one hydrogen atom, and the CH3 (methyl radical) 
becomes a positive radical, which enters into many combi- 
nations ; for instance, CH3CI (methyl chloride), CH3OH 
(methyl hydroxide), or CH3, CH3 (methyl methane), which 
is called ethane and is written C2Hg. This ethane may 
have one hydrogen atom substituted by CH3, also CH3, C2H5 
(methyl ethane, propane, C3Hg), which in turn may be 
again substituted, and so on. ( Vide Organic Chemistry.) 

The phenomenon of combustion is dependent upon 
three factors : first, something to burn ; second, a supporter 
of the combustion ; and third, a kindling temperature. 
We have learned that oxygen burns in hydrogen, and 
chlorine in hydrogen, so combustion is not essentially a 
process of oxidation. In everyday hfe, however, we regard 
combustion as the burning of such materials as hydrogen, 
coal gas, charcoal, coal, oils, fats, and so forth, in the 
air; in fact, an accelerated oxidation. If the combustible 
materials, gasified, are mixed with air and set on fire, the 
acceleration is so great that the combustion appears to be 
almost instantaneous, and an explosion results. AH chemi- 



CARBON HYDRIDES — FLAME — ILLUMINANTS 93 

cal actions are rendered sluggish at very low temperatures. 
Oxidation by the addition of oxygen proceeds at ordinary 
zero, but that is warm in comparison with — 184°. Com- 
bustion requires an even greater elevation of temperature, 
and once begun produces heat. The temperature at which 
it begins is called the kindling point. A mixture of hydro- 
gen and oxygen, or methane and oxygen, is harmless until 
the kindling point is reached. Metals conduct heat. If, 
therefore, a combustible mixture is kept separated by a 
perforated metal screen, as wire gauze, from a fire, no 
explosion results. Humphry Davy devised the safety 
lamp, which is used in coal mines, by the application of this 
principle, in response to the demands resulting from the 
colliery explosions in England. 

If the combustible substance is a gas which burns 
quietly, producing heat and more or less light, 2. flame is 
produced. When charcoal burns in the air, we get heat 
from its combustion, light from the incandescent solid, 
but little or no flame. If we burn an oil, we get heat from 
its combustion, light from the heated particles of evapo- 
rated liquid, and flame. If we light a candle, we melt 
some of the solid and the liquid acts as an oil. This may be 
readily shown by placing one end of a glass tube close to 
the wick, inside the flame, and inclining it at a small angle 
from the vertical. On placing a lighted match at the 
upper end of the tube, a flame is produced by the burning 
of the volatiHzed oil. When we set a stream of illuminat- 
ing gas on fire, we get a flame by its combustion in the 
air. This is a common practice. From a strictly scientific 
point of view it is immaterial whether we light gas in the 
air, or Hght air in gas. The important factor is the chemi- 
cal reaction of one gas with another. Heat is produced at 
that particular place, and the flame is made up of the mat- 



94 GENERAL INORGANIC CHEMISTRY 

ter there heated. Some gases, as hydrogen and methane, 
give flames that are almost invisible. The energy gener- 
ated practically all goes to the production of heat. If an 
infusible substance, like a platinum wire, Welsbach mantle,* 
or finely divided carbon, iron, or other dust, is brought 
into such a flame, it becomes limiinoics. The luminosity of 
the flame is not dependent so much upon the temperature 
as it is upon the density of the gas and the presence of 
solid particles, which are heated to incandescence. The 
presence of solid carbon in a candle or gas flame is readily 
shown by cooling the luminous portion by inserting a piece 
of cold porcelain. Soot is deposited. 

Illuminating gas is made by the destructive distillation 
of coal, when it is a mixture of combustible hydrocarbons, 
which burn with a luminous flame, or by the passage of 
steam over heated carbon. Gas produced by the latter 
method, water gas, is made up of hydrogen and carbon 
monoxide. These burn with a non-luminous flame. To 
render it suitable for illuminating purposes it is cai^buretted, 
i.e., gasified carbonaceous material is added, which, when 
decomposed in the first burning, liberates free carbon. 
This heated carbon gives luminosity. As this hot car- 
bon comes in contact with air, it is burned to invisible 
carbon dioxide. Therefore a gas flame has three zones, 
the innermost one being the first burning, which liber- 
ates carbon and is non-luminous. The middle zone is 
luminous ; and the outer one, where the combustion is com- 
pleted, is non-luminous. If the pressure is such as to 
force the gas from the tip at such a rate as to prevent 
sufficient air from coming into contact with the combust- 
ible constituents to complete the oxidation, a smoky flame 

* A Welsbach mantle is essentially a web of comparatively infusible 
oxides of thorium (99%) and cerium (1%). 



CARBON HYDRIDES — FLAME — ILLUMINANTS 



95 



results. This is obviated at the gas works by mixing a suit- 
able proportion of air with the gas in advance. This brings 
about proper combustion at the pressure the gas is delivered 
to the consumer. 

When gas is to be burned for heating purposes, lumi- 
nosity is not desired. Water gas is most suitable for heating, 
and it may be used to produce hght, if it is burned with a 
Welsbach mantle. Many consumers do not use the mantle, 
although many million are produced annually, and two 
series of gas mains would be too expensive. Bunsen 
invented a burner, a mechanical device for mixing sufficient 
air with the gas previous to its burning, which brings about 
such complete combustion of the constituents of the gas 
as to make it non-luminous. By regulating the inflow of 
air, the flame may be caused to assume varying degrees of 
luminosity. The Bunsen burner was first used with gas 
made from coal. The principle is now universally applied.* 

The blowpipe is a mechanical device for directing the 
flame, insuring the complete combustion of all constituents, 
with localization and consequent increase of heat. 

* Coal gas for house illumination was introduced in London by Murdock 
in 1792. By 1815 it was used in Paris, also, for street lighting. One ton of 
good gas coal yields about 10,000 cu. ft. of 16 candle power gas. The 
average composition of the four kinds of gas is shown in the following table : — 



Candle power 
lUuminants . . 
Marsh gas (CH4) 
Hydrogen . . 
Carbon monoxide 
Carbon dioxide . 
Nitrogen . . . 



Coal 

17-5 
5-0 
34-5 
49.0 
7.2 
I.I 
3-2 



Water 
(Fuel) 



I.O 

52.0 



6.0 

3-0 



Water 
(Carbiiretted) 

25.0 
16.6 
19.8 
32.1 
26.1 

3-0 
2.4 



PiNTSCH 

(Oil) 

65.0 

45 -o 

38.8 

14.6 (ethane) 



96 GENERAL INORGANIC CHEMISTRY 

EXERCISES 

1. Why do the hot coals of a wood-fire burst into flame when 
they are blown upon? Why is a lighted match put out by the 
same procedure? 

2. Explain the apparently redundant expression " oxidation by 
the addition of oxygen." 

3. Account for the brilliant light obtained when magnesium or 
phosphorus is burned. 

4. Why does a blowpipe give a higher temperature than a Bun- 
sen burner? 

5. Explain the phenomenon of flame. 



CHAPTER XV 
CARBON OXIDES — VALENCE 

Three compounds of carbon and oxygen are known, 
viz., CO2, CO, and C3O2. Each one of these presents in- 
teresting facts, and together they ilhistrate important prin- 
ciples. 

Carbon dioxide, CO2, m. wt. 44, is the first product in 
the combustion of coal and the final oxidation product of 
all compounds of carbon, especially in the processes of 
fermentation, decay, and respiration. It occurs in the air 
(about thirty tons over each acre), in volcanic gases, dis- 
solved in most spring waters, and, rarely, in cavities of 
quartz crystals. In some localities it issues from the 
ground in large quantities, and where topographic condi- 
tions are favorable it collects in low places, as in Poison 
Valley in Java and the Grotta del Cane near Naples. 
It is found combined with many metalHc oxides, forming 
carbonates, as limestone (CaCOg), strontianite (SrCOg), 
and siderite (FeCOg). 

Van Helmont (i 577-1644), who was the first to char- 
acterize various gaseous substances as different from air, 
called carbon dioxide *' gas sylvestre," the exact reason for 
which we do not know. Limestone (calcium carbonate, 
CaCOg) up to 1757 was regarded a simple substance. 
Black determined that carbon dioxide was given off when 
it was heated (in making quicklime), so he called it ''fixed 
air." As a water solution of carbon dioxide is acid in 
reaction, Lavoisier called it " acide carbonique." Dalton 

97 



98 GENERAL INORGANIC CHEMISTRY 

analyzed it also, as well as carbon monoxide. He observed 
the ratio of carbon to oxygen in the two compounds to be 
I : 2 and i : i, respectively. This relationship was one of 
those usqd by Dalton in determining the law of multiple 
proportions. 

It is prepared — 

First, by burning carbon and its compounds, between 
4- 400° and + 700° : 

C -1- 02->C02. 

Second, by decomposing a carbonate with an acid : 
CaCOg + 2 HCl -^ CaCl2 + H2O + \ CO^. 

Third, in the processes of fermentation large quanti- 
ties are produced, collected under pressure in steel cylin- 
ders, and used commercially. 

Carbon dioxide is absorbed by the leaves of plants from 
the air and is carried to the leaves in solution by the juices 
of the plant from the water in the soil. There under the 
influence of light and in the presence of chlorophyl, the 
coloring matter of the leaves, it is converted into more 
complicated carbon compounds, and oxygen is liberated 
through the stomata. An acre of oats liberates about the 
same amount of oxygen as it absorbs carbon dioxide in the 
growth and maturing of the plants. 

Carbon dioxide is a colorless gas, heavier than the air 
(sp. gr. 1.529), hence may be collected by downward dis- 
placement. Under 50 atmospheres pressure it is liquefied 
at ordinary temperatures (Faraday); at 36 atmospheres 
pressure and 0° it forms a white snow, which melts at 
— 78°. When the liquid is vaporized by diminishing the 
pressure, this snow is readily produced. The temperature 
of the snow is —60°. The solid is a poor conductor of 



CARBON OXIDES — VALENCE 99 

heat and vaporizes slowly. When it is evaporated in a vac- 
uum, a temperature of — 100° is attained. The liquid is 
colorless, with specific gravity of 0.91 ; specific gravity of 
the solid, 0.83. At the temperature of fusion of the solid 
the tension equals 3.5 atmospheres ; the liquid has that ten- 
sion at that temperature. If the pressure is less than 3.5 
atmospheres, no liquid is formed ; the solid vaporizes. 
Many other solids behave in this way. Ice melts at o'^ ; its 
tension is 4.6 mm. If the external pressure is lower, i.e., in 
vacuo, ice does not melt to water, but vaporizes at once. 

It is neither combustible nor a supporter of combustion. 
It extinguishes ordinary flames. Upon this property de- 
pends its use in fire extinguishers, as in hand grenades. 
Some very powerful combustions, however, can continue 
in it. Burning magnesium decomposes it : — 

2 Mg + CO2 I^ 2 MgO + C. 

Although, a very stable compound, it can be decomposed 
by an electric spark, and it dissociates partially into CO 
and O at +1300°. Glowing carbon reduces it to carbon 
monoxide : — 

c + co2l;:2CO. 

It is soluble in water, volume for volume. The water 
solution, " carbonic acid," is weakly acid, reddening blue 
Htmus paper. All natural waters contain more or less 
COg. The amount of CO2 absorbed by water varies with 
the temperature and the pressure, as gases are condensed 
in proportion to the pressure (Law of Henry and Dalton), 
One volume of water dissolves 2 volumes of CO2 at 2 atmos- 
pheres pressure, 3 at 3, and so forth. When this extra 
pressure is removed, the liquid effervesces through the 
escape of the excess of CO2. Upon this depends its use 
in effervescent drinks. 



100 GENERAL INORGANIC CHEMISTRY 

Carbon dioxide is not an active poison. Animals become 
asphyxiated in an atmosphere of it on account of the lack 
of oxygen. 

Carbon monoxide, CO, m. wt. 28. When in the combus- 
tion of coal the temperature reaches + 700° or higher, or 
the CO.2 produced at the lower temperatures comes into con- 
tact with more carbon, carbon monoxide is produced: — 

2C + 02->2CO, and C02 + C^2CO. 

Glowing coals at a moderate temperature burn without 
flame, but from + 1000° upward there is flame. The lam- 
bent blue flame observed over a hot anthracite coal fire is 
the carbon monoxide burning back to the dioxide : — 

2CO + 02:^2C02. 

On account of the non-luminous flame produced by its 
burning, carbon monoxide was mistaken for hydrogen for a 
long time. 

It may be prepared by the method cited above, or by the 
decomposition of certain compounds. For instance, formic 
acid has the formula H2CO2. If we treat it with a sub- 
stance which will abstract water, we obtain the monoxide : — ■ 

H2C02r±:H20 + t CO. 

It is prepared commercially, and used extensively, by 
passing steam over hot carbon (coke), " water gas" being 
produced : — 

C + H20^H2 + CO. 

Carbon monoxide is a colorless, tasteless, almost odorless 
gas. It has a specific gravity of 0.967 (i 1. weighs 1.25 g.). 
It is condensed to a Hquid, b.-p. — 190°. It is only slightly 
soluble in water, i .-30, and forms no acid with it, but is 
dissolved in a solution of cuprous chloride (CU2CI2), forming 



CARBON OXIDES — VALENCE lOI 

a crystalline compound, which is decomposed on heating, 
with the Hberation of the gas. It burns with a beautiful 
blue flame to carbon dioxide. It will remove oxygen from 
some metallic oxides when heated with them : 

CuO + COr=>Cu-f-tC02; 
Fe203H-3CO=>Fe2+t3C02. 

These reactions are utilized technically. It also reduces 
the salts of some metals, like gold and palladium, precipi- 
tating the free metal. Under the influence of gentle heat 
(+ 50°) it combines with certain metals, especially nickel, 
to form a gaseous compound, nickel carbonyl [Ni (CO)^], 
which on elevation of temperature (+ 250°), decomposes 
with the separation of the nickel and re-formation of the 
gas. The metal may thus be picked up in one place, trans- 
ferred as a gas, heated and deposited in another, and the 
transporting agent (CO) cooled and used over again 
(Process. of Mond for the extraction of nickel). 

Carbon monoxide is a direct and cumulative poison. 
The normal function of the hemoglobin of the blood is to 
form a compound with oxygen, oxy-hemoglobin. The 
last mentioned, in arterial blood, acts as a carrier of oxygen 
to the capillaries. Carbon monoxide combines with hemo- 
globin to produce a more stable compound, carboxy-hemo- 
globin, which gives the blood a bright red color, to be sure, 
but prevents the fulfillment of its function. When about one 
third of the hemoglobin has entered into combination with 
carbon monoxide, death results. The presence of 0.05 per 
cent of carbon monoxide in air that is breathed constantly 
is dangerous. Carbon monoxide readily passes through 
red-hot iron. Red-hot stoves or ovens, especially when the 
draught is closed and the ventilation poor, are often the 
causes of slight poisoning by carbon monoxide, as is 



I02 GENERAL INORGANIC CHEMISTRY 

evidenced by the dullness and headaches experienced 
by occupants of rooms where such conditions obtain. 
Carbon monoxide is produced in tobacco smoke and ex- 
hibits its toxic action after excessive smoking. 

By a complicated method a lower oxide, carbon suboxide, 
C3O2, may be obtained as a liquid at + 7° (Diels). It has 
a very penetrating odor and is solely of scientific interest. 

By a brief recapitulation of the hydrogen and oxygen 
compounds of some of the elements we have considered, 
most interesting relationships are observed. A molecule 
of hydrogen consists of two atoms. We may, for conven- 
ient illustration, write it, H — H. A molecule of hydrogen 
chloride is apparently the same, with i H substituted by 
I CI; H — CI. In CH^ we may substitute one or all four 
hydrogen atoms by chlorine, hence i H and i CI appear 
to be equivalent; that is, we may substitute atom. for atom. 
A molecule of water, H2O, may be written H — O — H. 
Later we shall learn of CI2O, which may be written 
CI — O — CI. Apparently i O requires 2 H or 2 CI as its 
equivalent for substitution. We have learned of the com- 
pounds HCl, H2O, H3N, and H^C. And as i O is equiva- 
lent to 2 H, we should be able to replace 2 H by i O ; for 
example, in H3N, HON (which is known) and in H^C, 
H2OC (which we shall learn about) and O2C (or CO2), 
which we have studied. This property of an element to 
substitute another, atom for atom, or a multiple, is known 
as valence. Hydrogen is the unit. When an atom of any 
element combines with one atom of hydrogen, or its equiva- 
lent, it is said to be univalent. If two atoms of hydrogen, 
or its equivalent, are necessary, as for oxygen, bivalent ; if 
three, as nitrogen, trivalent; if four, as carbon, quadriva- 
lent ; and so forth. 

This property of the elements is not inherent, but de- 



CARBON OXIDES — VALENCE 103 

pendent upon a number of conditions, and variable. For 

example, we have considered two oxides of carbon, CO2 

and CO. The valence of the oxygen or carbon must vary. 

If we write the compounds graphically, that becomes more 

H 

I 
apparent: H— C— H ; H— O— H; 0=C=0; C=0. 

I 
H 

The lines mean nothing more than a graphic illustration 

of the direction of the attractive force which holds the 

atoms together in the molecules. We know little of 

the actual structure of the molecule. When the element 

exhibits its highest valence (CO2), we say it is saturated ; 

when not (CO), iinsatiiratcd. The suboxide of carbon is 

easily explained in terms of valence in this manner ; 

0=C:=C=C=0, in which the carbon is consistently 

quadrivalent and the oxygen bivalent. 

As many of the elements form compounds with hydrogen, 

whose univalence, as far as we are aware, is constant, and 

nearly all of the elements form compounds with oxygen, 

about the bivalence of which there is only slight suspicion, 

we may classify the elements according to this property. 

EXERCISES 

1. How much carbon dioxide may be obtained from 22 g. cal- 
cium carbonate? 

2. Suppose two volumes of carbon monoxide were burned with 
oxygen, how many volumes of the latter would be necessary, and 
how many volumes of carbon dioxide would be produced? 

3. Why is it that liquefied carbon dioxide forms the solid as 
soon as it is exposed to atmospheric pressure? 

4. Explain the effervescence of carbonated waters. 

5. Illustrate what is meant by valence. 



CHAPTER XVI 
THE PERIODIC LAW 

Hydrogen was arbitrarily selected for beginning our 
study of the chemical elements. In continuing it certain 
resemblances were observed among the members of two 
separate groups, namely, the halogens and alkali metals. 
In looking for an orderly and systematic arrangement of 
facts, we classify on the basis of resemblance. Classifica- 
tion is most helpful as a guide in investigation, as relations 
are suggested among the facts observed and indications 
appear whereby new facts of more or less value may 
be secured. The immediate object of this chapter is to 
lay out a plan of the relationships of the elements, the 
pursuit of which will facilitate their further consideration. 

There have been presented so far four characteristic 
properties of all the elements. We shall therefore use 
them as bases for classification. 

I. CJiemical Affinity, or Quality of Combining Power. 
This is a primitive, permanent, constant force depending 
wholly upon the nature of the unchanged atom, and is 
characteristic of all atoms known, except the " noble 
gases," which appear to be devoid of it. These elements 
may, therefore, be set aside as one family. All evidences 
of chemical affinity among the other elements are accom- 
panied by other forms of energy, hence we have no way 
of measuring affinity. If we had means for measuring 
chemical affinity, as we may measure an electric current 
or heat, a permanent classification on this basis would be 
possible. We can roughly classify atoms by this property, 

104 



THE PERIODIC LAW 1O5 

however, as they vary widely in their chemical character ; 
for example, the halogens combine vigorously with hydro- 
gen and only by indirect means with oxygen ; the alkali 
metals act in the reverse way. Nitrogen combines with 
both, but not readily or directly with ease. 

2. Valence, or Quantity of Combining Power, as we have 
learned, means the ability of an atom to hold a certain 
number of other atoms in union, forming a compound. 
This bears no definite relation to the combining power, 
that is, whether strong or weak. Valence is not an in- 
herent property of any one atom, but, in part, it is depend- 
ent upon the influence the atoms have upon each other in 
compounds, and is variable. Nitrogen in ammonia is triv- 
alent (NH3). Ammonia combines directly with hydrogen 
chloride (HCl) to produce ammonium chloride (NH^Cl), 
in which compound the nitrogen is quinquivalent. Phos- 
phorus forms two compounds with chlorine and two with 
oxygen : PCI3 and PCI5, P2O3 and P2O5. The atoms may 
be classified, in a measure, according to the valence, but 
the classification is not based upon a fixed property. 

3. Electjv-chemical Character. We have seen that some 
binary compounds may be decomposed by an electric cur- 
rent, one constituent going to the positive and one to the 
negative pole (H2O, HCl, NaCl). Hence, we have electro- 
negative and electro-positive atoms. At one time the 
elements were divided into two great classes, the metals 
(electro-positive) and non-victals (electro-negative). In fact, 
this rough subdivision serves a good purpose even to-day. 
The non-metallic group includes boron, carbon, silicon, 
nitrogen, phosphorus, arsenic, oxygen, sulphur, selenium, 
tellurium, and the halogens. Some of them combined with 
hydrogen (HCl, HBr, H2S), some combined with hydroxyl 
[B(0H)3, ClOH], and the oxides of some combined with 



I06 GENERAL INORGANIC CHEMISTRY 

water (H2O, SO3 = H2SO4), produce acids. The oxides 
of the metals combined with water give hydroxides or 
bases [NaOH, Ca(0H)2, Fe(0H)3]. 

The difference in the intensity of the electro-chemical 
character of different elements is often very pronounced; as, 
for example, the alkali metals and the halogens are diamet- 
rically opposed to each other. Chlorine and iodine are 
both electro-negative, but the former replaces the latter in 
binary compounds, hence appears to be more strongly 
electro-negative. Sodium and silver are electro-positive, 
but the former is more so. In other words, there are 
different degrees of electro-positive and electro-negative 
properties. Furthermore, when hydrogen and arsenic 
combine (AsHg), arsenic is negative, but when arsenic 
combines with oxygen (AS2O3), arsenic is positive. There- 
fore, the electro-chemical character of an element is not 
absolute but relative. There is no unit of measure or 
standard known by which the electro-chemical property 
can be accurately determined. 

4. Classification by Ato7nic WeigJits. The atomic weight 
is a constant value determinable in terms of a standard, 
hence is fixed and, being capable of exact measurement, 
may be used in the classification of the elements. Any 
acceptable method of classification must, however, provide 
for the other three bases referred to. In 1863 Newlands 
arranged some of the elements in the order of the increase 
of the atomic weights, in this manner : — 



I 
Li, 7 


2 
Be, 9 


3 4 
B, II C, 12 


5 6 

N, 14 0, 16 


7 
F, 19 


8 

Na, 23 


9 

Mg, 24 


10 II 
Al, 27 Si, 28 


12 13 

p, 31 s, 32 


14 
CI, 35-5 


15 
K, 39 


16 
Ca, 40, 


and so forth. 







THE PERIODIC LAW 107 

All except half fractions in the values are ehminated for 
convenience. Hydrogen is omitted. It was observed that 
the eighth and fifteenth elements exhibited properties 
similar to the first ; the ninth and sixteenth similar to the 
second, and so forth. Newlands presented such a fantastic 
picture of the " law of octaves " in nature that his sugges- 
tion failed to receive serious consideration. 

In 1869, Mendelejeff, and the year following Lothar 
Meyer, independently, propounded the Periodic Law, 
which is based apparently upon the fact that all the 
properties of the elements are periodic functions of tJicir 
atomic weights. "^ We may secure a clearer understanding 
of this, if the elements are tabulated in a modified form 
(p. 108), but a thorough comprehension must await a further 
study of the elements. This much we may note, how- 
ever, the alkali metals appear in one column, so do the 
halogens. They stand at the extreme ends of the table, 
which may serve to show their marked difference in electro- 
chemical properties. The heavy zigzag hne in the upper 
right-hand corner also serves to mark off the so-called non- 
metals. Furthermore, it will be noted that two elements 
are marked with an asterisk (*), namely yttrium and 
indium. The places occupied by these two elements were 
blank when Mendelejeff made his table. The elements 
were known, but they were regarded as bivalent, with 
an equivalence of 29+ and 38+ respectively, or atomic 
weights of 58+ and 'j6'^. As there were no places in the 
table for elements with such values, Mendelejeff said 
that the values were wrong. Investigation subsequently 
showed he was right and that they are trivalent, hence the 

* A complete history of the inception and formulation of this important 
generalization is had in "The History of the Periodic Law," Venable, Chemi- 
cal Pubhshing Co. 



io8 



GENERAL INORGANIC CHEMISTRY 



fx, C^ 




W 


^ 












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c/^ ^o 


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On 










^ ^ 


^ P. 


< 




7 8 

CO « 




s 


00 




u ^ 




* o 




CO n; 




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8 




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—1 r^ 


tS 


o 


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THE PERIODIC LAW 169 

accepted atomic weights became three times the equiva- 
lence, or 89 and 115, respectively. 

Again the places marked with the double asterisk (**) 
were blank. Considering the positions among the known 
elements occupied by these "blanks," Mendelejeff predicted 
not only their discovery, but foretold their properties with 
surprising accuracy. 

According to the statement of the law, if we know the 
atomic weight, we should be able to place the element in 
the ascending scale, and its properties should accord with 
its location. It happens, however, that the facts as they 
have been observed are not always in accord with this 
statement. Cobalt has a larger atomic weight than 
nickel, and tellurium has a greater value than iodine, yet 
they are placed ahead of those elements in the table. 
This was done on account of the known physical and 
chemical properties of these elements, which indicated 
their fam^ily relationship. In a way, therefore, they must 
be regarded as exceptions to the law, for the time being at 
least, although so far no satisfactory mathematical relation- 
ship among the figures representing the atomic weights 
has been secured. 

We are now ready to look at the most modern table, 
which will be followed, in a measure, from now on (p. no ). 

In this compact table several important points are to be 
noted. First, the valence in terms of hydrogen increases 
(as indicated) from Group I to Group IV, and then decreases 
to Group VII. The valence in terms of oxygen increases 
consistently through Group VIII. The last group (VIII) 
contains those elements with atomic weights close together, 
and which resemble each other physically and chemically 
to a marked degree. Second, as the *' noble gases" show 
no valence, they are placed in a separate Group O. Third, 



no 



GENERAL INORGANIC CHEMISTRY 



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(N) 

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Oho 



THE PERIODIC LAW III 

certain of the rare elements, the compounds of which are 
fairly well known, are placed in the table where the atomic 
weights call for them. Yet some of these elements are 
not placed at all. Fourth, hydrogen is placed in a horizontal 
period (Group I, Period I) alone, as there is no other 
place for it, and it fits the position. Fifth, the table satis- 
fies the demands of classification by chemical affinity, 
valence, and electro-chemical properties, which facts will 
become apparent in due time. 

The first period of seven (horizontal line 2) contains the 
group elements, or bridgc-clcmcnts, since they show many 
close analogies to the elements in the immediate neighbor- 
ing groups, while the second period (line 3) gives us the 
type-element of the group. The properties of the other 
members may usually be defined by their differences from 
the type. The vertical group then branches into two 
series, a positive (left) and negative (right). For example. 



Li 

1 


and 

1 


1 

Na 

/\ 

K Cu 

1 1 


1 

S 
/ \ 

Cr Se 

1 1 


1 1 
Rb Ag 


1 1 
Mo Te 



Cs Au etc. 

On the positive side, the members of the positive series 
show a close relationship to the type-element, while in the 
negative groups those in the negative series are more hke 
the type. As we pass down the electro-positive series, that 
property becomes more pronounced. Caesium is the most 
positive of the alkali metals. As we pass down the electro- 
negative series, that property becomes less pronounced. 
Bromine, while electro-negative, is less so than chlorine. 



112 GENERAL INORGANIC CHEMISTRY 

Iodine is even less so ; in fact from its physical properties 
it appears metallic. 

No human document is perfect ; this is, however, the 
best classification of the elements we have at present. Cer- 
tainly the reader will find it most useful, as he gradually 
becomes familiar with it and observes not only the kinship 
of the elements, but the attractive fields awaiting further 
investigation. The periodic law is one of the most im- 
portant of the recent generalizations, and has been of the 
greatest service in the study of the chemical elements and 
their compounds. 

EXERCISE 

Refer to the chapters on the halogens and alkali metals, trace 
their resemblances, and note the gradation of properties. 



CHAPTER XVII 

GROUP VI. — NEGATIVE SERIES : OXYGEN, SULPHUR, 
SELENIUM, TELLURIUM 

These elements are bivalent toward hydrogen, giving the 
compounds H^O, HgS, H2Se, and H2Te ; and quadrivalent 
or sexivalent toward oxygen, OO2, SOg, SO3, Se02, Te02, 
Te03. Oxygen having been discussed, we may consider 
sulphur. 

SiilpJuLr, S, at. wt. 32.06, has been known since ancient 
times. Sulphur (brimstone) occurs free near volcanoes, 
especially near Mt. Etna, mixed with gypsum and other 
minerals, and in the pores of pumice stone. Large 
deposits have also been found in Louisiana. It occurs 
combined as sulphides, as iron sulphide (pyfite, FeS2), 
galena (PbS), zinc blende (ZnS), or with oxygen and a posi- 
tive element in the form of sulphates, as gypsum (CaSO^) 
and barite (BaSO^). It is present in all albuminoid sub- 
stances of animal and vegetable matter. Some bacteria 
and algae contain as much as one fourth by weight of sul- 
phur. Sulphur occurs in abundance and is widely distrib- 
uted, but is present in very much less amount than oxygen. 

It is prepared by three methods : — 

I. From the native sulphur by melting in kilns, repuri- 
fying by distilling and casting in wooden molds (rolled 
sulphur or brimstone), or by conversion into a vapor and 
chiUing in large brick chambers to a fine yellow powder 
(^flores sulpJiuris), flowers of sulphur. There are different 
methods for melting the sulphur out of the crude ore, an 

113 



114 • GENERAL INORGANIC CHEMISTRY 

important one depending upon immersion of the ore in 
a liquid (a water solution of calcium chloride) which 
boils at a higher temperature than the melting point of sul- 
phur. The method which made the Louisiana deposits 
available depends upon heating the rock deep down by 
means of superheated or high-pressure steam. The sulphur 
is melted and then forced to the surface mingled with hot 
water. It is sometimes dissolved in a suitable solvent, 
which is evaporated and used again. 

2. Sulphur is also obtained, in small quantities, by heat- 
ing certain of the natural metalHc sulphides without the 
presence of air, as pyrites : — 

FeS2 = FeS 4- S. 

3. Sulphur is recovered from certain waste sulphides in 
manufacturing processes by converting the solid into H2S 
and decomposing that, with oxygen and heat, by means of 
a catalytic agent, into H2O and S. 

Properties. At ordinary temperatures it is usually a yel- 
low, almost odorless, brittle solid. It melts at + 115° to a 
thin, amber hquid (SX), becoming dark brown and viscid at 
+ 250° (Sft) and again a fluid at + 300°, boihng at + 445°. 
At + 500° it appears to have eight atoms in the molecule, 
while at -f 1000° two atoms. 

It is insoluble in water, but readily soluble in carbon 
disulphide and sulphur chloride. It is a strongly electro- 
negative element, combining with positive elements to form 
sulphides, as PbS, ZnS, FeS, and so forth. Finely divided 
metals, except some of the *' noble" ones, when rubbed 
with sulphur, give sulphides, as HgS. In these com- 
pounds with metals S is bivalent. It burns with a blue 
flame in oxygen, forming SO2 ; when oxidized in the 
presence of water, sulphuric acid, a derivative of SO3, is 



NEGATIVE SERIES: OXYGEN, SULPHUR 115 

formed. Sulphur combines with chlorine directly. In 
combining with non-metals, like oxygen, it shows variable 
valence, the maximum being sexivalent. 

Four allotropic forms of sulphur are known : — 

1. OctaJiedraJ^ or Rhombic, Sulphur. This is the ordi- 
nary, native, and stable form; sp. gr. 2.07; soluble with 
difficulty in alcohol and ether; more soluble in ethereal 
oils and the hydrocarbons ; and very soluble in S2CI2 and 
CS2. One hundred parts of the latter will dissolve 46 of 
sulphur at +22°. It fuses at +114.5°. It becomes 
charged negatively when rubbed with wool. 

2. Prismatic, or Monocliiiic, Sidphur. When sulphur is 
melted and allowed to cool slowly, long, transparent, 
needle-like crystals are produced, having the sp. gr. 1.96 
and m.-p. + 120°. This changes to the first variety on 
standing. A substance which under proper conditions 
exhibits two states of aggregation, crystalline forms, is 
dimorpJions. 

3. Plastic, or Insoluble, Sulphur. When sulphur is 
boiled and suddenly cooled by pouring into water, it 
becomes plastic, elastic, and without crystalline form, with 
sp. gr. 1.92. Only a part of the mass is soluble in CS2. 
That which is insoluble is the viscous S/^t in a supercooled 
state (Alex. Smith). On standing, the rubber-like form 
becomes brittle and returns to the stable form. 

4. Milk of Sulphur {lac sulphiiris). When a strong acid 
is added to potassium polysulphide, this reaction takes 
place : — 

K2S5 + 2 HClrr>2 KCl +tH2S +|4 S. 

This precipitated form of sulphur is white and finely 
divided, and is sometimes used in medicine. 

Sulphur is used in the manufacture of sulphur dioxide 



Il6 GENERAL INORGANIC CHEMISTRY 

and sulphuric acid, gunpowder, matches, in vulcanizing 
rubber ; in medicine as a parasiticide and gentle laxative ; 
also in various compounds. 

Seleniinn {aekrjvr] — the moon), Se, at. wt. 79.2, was dis- 
covered by Berzelius in 18 17. It occurs in much smaller 
quantities with sulphur in certain pyrites (in dust flues of 
pyrites burners connected with sulphuric acid works), and 
also free. It has been found in many places, but is not 
very abundant. 

Selenium has also been had in several modifications. 
When obtained by treatment of a compound with sulphur 
dioxide, it is a red, brownish powder, soluble in CS2. It 
crystallizes from CS2, giving red crystals of sp. gr. 4.5. It 
melts at + 217°, boils at + 660°, giving a yellow vapor. 
When the fused mass is suddenly cooled, a portion separ- 
ates as a black substance. When the amorphous variety 
is heated to about + 100°, its temperature suddenly rises 
to about + 200°, and it changes to a dark, clear crystalline 
substance, with sp. gr. 4.8. It has a metallic luster, is in- 
soluble in CS2, and is a conductor of electricity, which 
conductivity is increased on exposure to light (Ruhmer 
lamp). At -f 1400° it has two atoms in the molecule. It 
resembles sulphur very closely, burning with a blue flame, 
the fumes having the odor of decaying horse-radish. It is 
less powerfully electro-negative than sulphur. 

Tellindum {tcllns — the earth), Te, at. wt. 127.5, v/as dis- 
covered by Muller von Reichenstein in 1782. It is found 
native and in certain gold ores and as sylvanite. It is 
precipitated by SO2 as a black powder, with sp. gr. 5.9. 
When fused, it forms a silvery white solid with a metallic 
luster; sp. gr. 6.4; m.-p. + 454° ; b.-p. + 1390°. It con- 
ducts electricity and burns with a blue flame. At -\- 1700° 
its vapor has two atoms in the molecule. 



NEGATIVE SERIES: SELENIUM, TELLURIUiVI 117 

According to the periodic law, tellurium should have an 
atomic weight of approximately 125, or iodine should show 
a value above that of tellurium. Numerous efforts to show 
that tellurium is complex, that it contains another element, 
heavier (at. wt. 214), -which would bring tellurium to a 
lower figure, have been made in vain (Brauner, Norris, 
Lenher). The same has been true of all efforts to find 
a lighter element in iodine, which would make the value of 
real iodine sufficiently high to be above that of tellurium 
(T. W. Richards). At present we simply acknowledge a 
defect in the lazv. 

EXERCISES 

1. What is the molecular weight of rhombic sulphur at ordinary- 
temperatures? 

2. What is the molecular weight of sulphur, selenium, and 
tellurium above + i 700° ? 

3. Tabulate the physical properties of the four elements con- 
sidered in this chapter, and state any general principles that may 
be drawn from the facts so collated. 



CHAPTER XVIII 

GROUP v. — NEGATIVE SERIES: NITROGEN, PHOSPHORUS, 
ARSENIC, ANTIMONY, BISMUTH 

These elements show little physical resemblance, but 
have much in the way of chemical properties in common. 
This we shall observe especially when we study their com- 
pounds with hydrogen, the halogens, and oxygen. 

ISiitrogeji has been considered. 

Phosphorus was discovered in 1669 by the merchant- 
alchemist Brand, who distilled the residue from evapo- 
rated urine. Gahn found calcium phosphate [Ca3(P04)2] 
in bones, and Scheele separated the phosphorus from it. 

On account of its strong affinity for oxygen, phosphorus 
always occurs combined with it in phosphates, as apa- 
tite, Ca5(P04)3F. It occurs widespread in small amounts 
in rocks and soils, from which it is taken up directly by 
plants and indirectly by animals. It is found in the ashes 
of cereals. Large phosphate deposits are found in South 
Carolina, Florida, Canada, Algiers, Spain, and Japan. 
Calcium phosphate constitutes more than three fourths of 
the mineral matter of bones. 

It is prepared by mixing the ground phosphate with 
carbon and sand and heating : — 

Ca3(P04)2 + 3 Si02 + 5 C ^ 3 CaSi03 + t 5 CO f f 2 P. 

This is best accompHshed by feeding the mixture continu- 
ously into a retort near the bottom of which are the ter- 
minals of a powerful alternating current, which is thermal 

118 



NEGATIVE SERIES: NITROGEN, PHOSPHORUS 119 

in its action. The calcium metasilicate (CaSiOg) fuses 
and runs to the bottom, from which it is drawn off from 
time to time. The CO and vapors of P pass out through 
pipes near the top and are bubbled through water. The P 
is liquefied, settling in the water, and the escaping CO 
is burned. The phosphorus is melted in warm water, 
strained through chamois, and cast in glass or tin molds. 
It is absolutely necessary to avoid the mixing of any air or 
oxygen with the vapor of phosphorus. 

Three allotropic forms of phosphorus are known ; the 
properties are conveniently compared in tabular form : — 



Yellow 


Red 


Metallic 


[Brand (1669)] 


[Schrotter (1845)] 


[Hittorf] 


Pale yellow 


Chocolate red 


Lustrous 


Strong odor 


Odorless 


Odorless 


Sp.gr. 1.83 


2.20 


2-34 


Phosphorescent 


Not 




Translucent 


Opaque 




Soluble in CS2 


Insoluble 




Subject to slow com- 






bustion 


Not 




Melts at +44° C. 


About +255^0. 




Changes to red 


Changes to yellow 




+ 3oo°C. 


+ 260° C. 




Soft 


Hard 




Flexible (ord. temp.) 


Brittle 




Poisonous 


Harmless 




Rhombic crystals 


Hexagonal 


Needles 


Takes fire +40^ C. 




, 


or with friction 


Stable form 




Boils +287^0. 







The phosphorus molecule, which is dissociated above 
+ 1040°, has four atoms in it. The yellow variety is insol- 



120 GENERAL INORGANIC CHEMISTRY 

uble in water, but soluble in oil of turpentine and carbon 
disulphide. It is very poisonous in the finely divided form 
or as a vapor. In chronic poisoning by phosphorus the 
teeth are affected and necrosis of the jaw-bone is produced. 
It combines readily with oxygen to form P2O3 or P2O5, 
burning with a green flame. It combines vigorously with 
the halogens ; causes precipitation of metals in copper 
sulphate and silver nitrate solutions. At ordinary temper- 
atures it oxidizes slowly with luminosity in the dark, hence 
its name. Its phosphorescence is not observed when it is 
under great pressure or in pure oxygen, unless the pressure 
is reduced to about 150 mm. As it is so readily oxidized, 
it must be kept under water. Great care must be taken 
in handUng yellow phosphorus, as serious burns may 
result. It takes fire spontaneously when left exposed to 
the air. It should not be rubbed in drying it, but gently- 
pressed with blotting paper. The yellow form on exposure 
to light becomes covered with a coating of the red form. 
This is an exothermic change (4-19.2 cal.). 

The yellow variety was at one time used in making 
matches, but its use for such purposes is now much re- 
stricted by law. It is used in making organic compounds 
and vermin paste. The red form is used extensively in 
making matches, the heads of which are frequently com- 
posed of red phosphorus and potassium chlorate bound 
together with glue. *' Safety " matches often have the 
heads made of antimony sulphide (SbgSg), potassium chlo- 
rate, and glue. The surface upon which they are rubbed 
to ignite them is composed of sand (or emery), manganese 
dioxide (Mn02), and red phosphorus. 

Ai'senic occurs free in nature, its metal-like properties 
having been observed by the alchemists. It is found more 
abundantly with sulphur and combined with metals, as 



NEGATIVE SERIES: ARSENIC l2l 

realgar (AsS), orpiment (AS2S3), arsenopyrite (FeAsS), 
lollingite (FeAs2). Lately it has been reported as a 
constituent, in very minute amounts, of the animal body 
(Gautier). 

When we heat a binary compound of sulphur or arsenic 
in the air, the sulphur is burned to a gas, sulphur dioxide 
(SO2), and arsenic to a white solid, arsenic trioxide (AS2O3), 
which subKmes at the temperature it is formed. By 
cooling the gases evolved the arsenic trioxide condenses as 
a white flour. This process of oxidation to remove volatile 
constituents is technically known as roasting. In the case 
of arsenical pyrites the reaction takes place as follows : — 

2 FeAsS + 5 O2 -t Fe203 + AS2O3 + t2 SO2. 

The iron oxide remains in the roasting furnace, the sul- 
phur dioxide is sent into the air or saved by methods 
referred to later, and the arsenic trioxide is collected by 
cooling. The escaping gases are passed through thin- 
walled chambers, usually wooden houses built with the 
weather boarding inside the rafters and studs. The 
"arsenic flour" is mixed with carbon and placed in iron 
kettles, built up of sections and provided with long thin- 
walled exit tubes to insure thorough cooling of the gases 
given off. 

AS2O3 + 3 Cr±2 As -f f 3 CO. 

Many thousand tons of iron pyrites are annually roasted 
in the manufacture of sulphuric acid. Arsenical pyrites is 
a constant and usually small impurity of the iron pyrites. 
Most of the arsenic trioxide collects as dust in the flues, 
but some of it is swept on, and constitutes an impurity in 
the acid and in many products subsequently obtained by 
the use of the acid. 

Arsenic is known in three modifications. One is an amor- 



122 GENERAL INORGANIC CHEMISTRY 

phous, black, brittle solid; sp. gr. 4.71. When heated to 
+ 360°, it changes into the second form, which is steel-gray, 
with metallic luster; sp. gr. 5.73, There is also a yellow 
variety soluble in carbon disulphide. At + 450° it sub- 
limes with a yellow vapor. At + 1700° it has two, while 
at + 700° it has four, atoms in the molecule. It is not 
changed in dry air, but takes fire at -f 180°, burning with a 
blue flame, forming AS2O3, which as a vapor has a garlic- 
like odor. It is insoluble in water and the ordinary 
solvents. It is a weakly negative element, combining 
with positive elements to form arsenides ; also with more 
negative elements like chlorine, sulphur, and oxygen. 

Arsenic is used in making its compounds and in certain 
alloys; i : 1000 of lead makes it hard. "Chilled " shot is 
made from this alloy. 

A7itimony. Basil Valentine, about the end of the fif- 
teenth century, first described the preparation of the metal. 
This was not a new discovery, however, as some of its 
compounds have been known from the earliest times, and 
used as pigments. Pliny refers to stibnite as stibium. The 
native sulphide, or stibnite, was called *' kohl " in Arabic, 
which was gradually changed to " alkol " and later to 
"alkohol." In the Middle Ages the term was applied to 
almost any fine powder, and later spirits of wine. 

The occurrence of antimony is similar to arsenic. They 
often occur together. It is found free and as stibnite, 
Sb2S3. It is not very widely distributed and is not so abun- 
dant as arsenic. 

It is prepared in the same way that arsenic is and also 
by heating the sulphide with iron : — 

Sb2S3 -f- 3 Fe = 3 FeS + 2 Sb. 
The iron sulphide and antimony melt and form two 



NEGATIVE SERIES: ANTIMONY, BISMUTH I-23 

layers, the antimony sinking to the bottom of the furnace, 
from which it is tapped from time to time. 

Antimony is a hard, brittle, steel-gray, brilliant, metallic, 
lustrous, leafy," crystalline solid, with sp. gr. 6.^, m.-p. 
+ 432°. When heated from + 1500° to + 1700°, it has two 
atoms in the molecule, while below that it is Sb^. It burns 
readily in the air, with a blue flame. With the positive ele- 
ments it forms alloys, especially type-, stereotype-, and 
britannia metals. Antimony alloys expand on solidifying, 
hence give very sharp castings. It combines readily with 
negative elements and forms a compound with hydrogen. 

Bismuth was first described by Basil Valentine, but was 
probably known earlier. 

Bismuth occurs free, but not widely distributed, and not 
abundantly; and combined as oxide (61203), sulphide (61283), 
and in small amounts in many nickel and silver ores. 

It is prepared by melting away from the veinstone with 
which it is found. 

It is a reddish-white lustrous metal ; crystalline and 
brittle, although slightly workable. It does not burn easily, 
but heated to kindling temperature in the air, forms Bi203. 
It combines chiefly with the negative elements. It forms 
alloys with low melting points. These alloys are used for 
safety plugs in steam boilers and sprinklers. 

EXERCISES 

1. What principles are illustrated by the methods given for the 
extraction of arsenic, antimony, and bismuth from their ores? 

2. In what ways do the physical properties of the members of 
this series change as the atomic weights increase ? 

3. Why is it so essential to avoid mixing air with phosphorus 
vapor ? 

4. What is the principle involved in roasting? 



124 



GENERAL INORGANIC CHEMISTRY 





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CHAPTER XIX 

GROUP II. — POSITIVE SERIES: ALKALINE EARTH 
ELEMENTS 

We have now studied all of the so-called non-metallic 
elements, except silicon, which is intermediate. Its con- 
sideration may be conveniently postponed a few pages, 
while we study the metals in logical sequence, taking those 
with dominating electro-positive properties first. The posi- 
tive series of Group I (the alkali metals) has received at- 
tention. The positive series of Group II contains what 
are spoken of as alkaline eartJi elements, because they 
resemble the alkalies, on the one hand, and the earths 
(Group III), on the other. 

This group of elements is of singular interest. First, 
because we have two names for the first member. Second, 
because that member is prepared by a type-method, which 
has been and is still extensively used in the preparation of 
the rarer metals. Third, because four members (mag- 
nesium, calcium, strontium, and barium) occur naturally in 
similar compounds (carbonates and sulphates), and were- 
known and mistaken for each other for a long time. Their 
oxides were regarded as elements up to a century ago. 
They never occur free in nature. Fourth, all of them are 
constantly bivalent and form binary compounds with electro- 
negative elements, XO, XCI2, XBrg, and so forth. And 
fifth, the heaviest member of the group has been known 
only a decade and possesses properties (in its compounds — 
we do not know the free element) which are causing a re- 

125 



126 GENERAL INORGANIC CHExMISTRY 

casting of many of the fundamental concepts of the science 
of chemistry. 

Berylli2L7n (glucinum) occurs in the mineral beryl 
[BeaAl/SiOg)^]. 

It is prepared by heating the halogen compound with a 
more strongly electro-positive element : — 

BeClg + Nag ^ 2 NaCl + Be. 

This method is applicable to at least the first five members 
of the series. 

This rare metal looks like the familiar magnesium. The 
compact form does not readily oxidize on heating to a high 
temperature, but when finely divided it burns with great 
brilHancy. The salts soluble in water have a sweet taste, 
hence the alternate name. Other metallic salts are also 
sweet ; therefore, if there were no other reason, preference 
should be given to the more distinctive name. 

Magnesium. Black first pointed out the distinction be- 
tween magnesium and calcium oxides. Its compounds 
are widely distributed and are more or less abundant, as 
magnesite (MgCOg), dolomite (MgCOg, CaCOg), and sili- 
cates, as meerschaum, talc, soapstone, olivine, and asbes- 
tos. Sulphates and chlorides occur in sea water and in 
certain salt deposits. 

It is a malleable metal, tarnishes in the air slowly at 
ordinary temperatures ; at an elevated temperature it burns 
with a brilliant, white light, which is rich in so-called 
chemical or actinic rays. The temperature of burning 
magnesium is between -f 1300° and -f 1400°. The in- 
tense light comes in large part from the chemical energy 
involved, for if it were due to incandescence, a temperature 
of at least + 5000° would be necessary to produce light 
of that character. Heated magnesium combines directly 



ALKALINE EARTH ELEMENTS 127 

with nitrogen to form the nitride (Mg3N2) ; therefore, when 
magnesium is burned in the air, the oxide produced is 
mixed with nitride. 

On account of its strong affinity for oxygen, magnesium 
is used to reduce some of the oxides of the rare metals. 
It is readily soluble in acids. Mixed with potassium 
chlorate, it is used for flash-lights. 

Calcium was first isolated by Davy by means of the direct 
electric current, and all these metals are now so prepared 
commerciall}^ 

It occurs as carbonate (limestone), sulphate (gypsum), 
fluorspar (CaF2), and in numerous silicates and phosphates. 
It is widely distributed and abundant. It is found in 
plants, and its compounds are constituents of the bones and 
shells of animals. 

It is a little harder than lead, may be cut, rolled, and 
drawn. It decomposes water at ordinary temperature, 
evolving hydrogen. When heated to redness in the air, 
it burns with a brilliant, orange-yellow flame (CaO). Some 
nitride (Ca3N2) is also produced. It combines directly with 
hydrogen also (CaHg), to form a compound commercially 
known as "hydrolyte." 

Strontiinn occurs as carbonate (strontianite) and sul- 
phate (celestite). 

Barium also occurs as carbonate (witherite) and sul- 
phate (heavy spar). 

Radiiun occurs in compounds, the exact combination 
being unknown. It will be considered in a special 
chapter. 

EXERCISES 

1. Give the two type-methods for preparing the alkaline earth 
metals, and the principles upon which they are based. 

2. From the table of comparative properties, observe the re- 
lationship of the specific gravities and atomic weights 



128 



GENERAL INORGANIC CHEMISTRY 



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41 



CHAPTER XX 

GROUP III. — THE EARTH ELEMENTS — THE RARE-EARTH 
ELEMENTS 

In this group we are introduced to elements which pre- 
sent several interesting features. First, these elements are 
primarily metallic in character, yet the oxygen compound 
of boron is acidic. Aluminum oxide acts as an acid oxide 
with strong bases, and as a basic oxide with strong acids. 
Second, the bridge-element is had in a form strikingly 
Hke the diamond, and the oxide of aluminum in general 
physical properties is similar to the magnesium oxide. 
Third, aluminum ranks third in the relative abundance of 
the elements, and its oxide, especially when combined 
with the oxide of silicon, gives us what is termed earth. 
Fourth, aluminum is the Hghtest metallic element of ex- 
tensive technical use. Fifth, elements are found in this 
group which confirm the periodic law, yet some are men- 
tioned that cause us to wish for a more perfect expression 
of the relationship of the members of the family of ele- 
ments. 

The elements of this group all show a valence of three 
toward oxygen, X2O3, and with the halogens, as BFg, 
LaClg, and so forth. None of them occurs free in nature. 

Boron occurs always combined with oxygen and hydrogen, 
as in boracic or boric acid, or its salts, as borax (NagB^O^, 
10H2O), boracite (2 MggBgOjg, MgCl2), and colemanite 
(Ca2B60ii,5H20). 

129 



I30 GENERAL INORGANIC CHEMISTRY 

It is prepared by reducing the oxide with a metal, as 

(i) B203H-6Nar:>3 Na20 + 2B, and 
(2) B203+3Mg^3MgO + 2B. 

It ignites at + 700° ; dissolves in melted aluminum, 
from which it crystallizes on cooling as dark, briUiant 
crystals (sp. gr. 2.6) which resemble the diamond in luster 
and hardness. It burns with even greater difficulty than 
the diamond. 

Boron is one of the few elements that combine directly 
with nitrogen. Boron nitride (BN) is formed. It com- 
bines with positive elements in the electric furnace, giving 
borides, some of which are of commercial importance. At 
high temperatures it combines with sulphur and chlorine. 

Ahimimun exists in abundance in compounds, but the 
difficulty of separating it prevented its early discovery. 
Soon after 1800 it was recognized that clay contained a 
new element. In 1827 Wohler isolated it. 

Aluminum always occurs combined, as with oxygen and 
silicon in clay ; in many minerals, as feldspar and mica ; 
in many forms of its one oxide, AI2O3, as corundum or 
emery. It is the chief constituent of many precious stones, 
like the ruby and sapphire ; and of cryolite (3 NaF, AIF3) 
and bauxite (AI2O3, 2 H2O). 

The principles involved in the preparation of aluminum 
present interesting applications of the science of chemistry 
to industry. It was made for years by the action of 
metallic sodium upon a double halogen salt : — 

AICI3, NaCl + 3 Na z:> 4 NaCl + Al. 

AICI3 does not melt, but sublimes, when heated under at- 
mospheric pressure. When mixed with NaCl, it readily 
melts. The problem of producing cheaper metallic alu- 



THE EARTH ELEMENTS 1 3 1 

minum therefore depended upon cheaper sodium. Cast- 
ner solved this problem. The price of the metal was 
reduced, but scarcely was this accomplished before Hall 
discovered that alumina (AI2O3), which is very insoluble, is 
soluble in a molten double halide, cryohte (AIF3, 3 NaF), 
and in that condition could be electrolyzed. Cells with 
carbon hnings acting as cathodes hold the cryolite, which 
is fused by the passage of a direct current (5 to 6 volts). 
Aluminum oxide dissolves in the bath. Carbon rods act 
as anodes and are oxidized by the escaping oxygen, while 
the freed metal collects as a liquid in the bottom of the 
cells and is drawn off from time to time. 

Aluminum is a white, silvery, lustrous metal. It melts 
at + 660°, but does not vaporize. It is the Hghtest metal 
of structural importance (sp. gr. 2.7). It is fairly tena- 
cious, malleable, and ductile, having about the same 
softness as silver. It is difficult to turn on the lathe or 
cut with a file as it adheres to and clogs the tools. It con- 
ducts heat and electricity. It does not conduct as well as 
copper when we compare cross sections, but weight for 
weight it is a better conductor. It is not sonorous when 
pure. Usually it is impure, however, and is then sono- 
rous. It does not tarnish readily, not being acted upon 
by pure oxygen at ordinary temperatures. Under some 
conditions it tarnishes, but the thin film of oxide formed 
prevents further oxidation or pitting. It combines with 
oxygen at high temperatures and thus reduces other sub- 
stances, liberating free metals. The Goldschmidt alumi- 
no-thermic process depends upon this property and is of 
great practical value. A mixture of aluminum powder 
and ferric oxide (thermit) is ignited by means of a burning 
magnesium wire : — 

Fe.303 + Al2 z^ A1203 + 2 Fe. 



132 GENERAL INORGANIC CHEMISTRY 

The temperature attained is about + 3000°. The iron 
melts, runs to the bottom of the vessel, and is tapped off, 
and the lighter fused AI2O3 forms a protective coating. 
Very pure metallic preparations are also made from such 
refractory oxides as those of chromium and manganese. 
The sulphides are reduced in the same way. The metal 
is soluble in acids, as vegetable acids, and especially in the 
presence of salts : — 

2 Al + 6 HCl r^rAl^Cle + f 3 H2. 

It is also soluble in certain alkalies : — 

2 Al + 6 KOH ::z^ 2 K3AIO3 + f 3 ^3. 

Aluminum is used for very many purposes where a 
light metal is desirable, as, for instance, in scientific instru- 
ments, domestic utensils, military accouterments, and air 
ships ; especially is it used for these purposes in the form 
of alloys, the most important of which are magnaUum, an 
alloy with (6 to 30 per cent) magnesium, aluminum bronze 
(5 to 12 per cent aluminum), which is easily fusible, of 
golden luster, with mechanical and chemical resistance 
superior to ordinary bronze. 

The Rare-eartJi Metals. This group, in both series, as 
may be seen from the two tables, contains several rare 
elements. The metals of the rare-earths are little known. 
Many of their compounds exhibit such similarity in chemical 
conduct that they are difficult of separation. They are 
found in rare and very complex minerals, especially gado- 
linite, euxenite, samarskite, monazite, which are found 
mainly in Sweden, Greenland, United States, and Brazil. 
Those in this group have so far shown no properties which 
have caused a commercial demand for them. The high 
prices quoted in the market for them are largely fictitious 



THE RARE-EARTH ELEMENTS 1 33 

values. These elements are interesting because one of 
them, yttrium, had its atomic weight revised in the work- 
ing out of the periodic law, two of them, scandium and 
gaUium, were predicted by Mendelejeff in applying the 
law, and their hidden possibiHties await further investi- 
gation. 

Other of the rare elements are even less known, victorium, 
thulium, holmium, and so forth, and we do not now know 
where to place them in the natural system. Either our 
knowledge of them is too meager, which is very likely, or 
the periodic law requires further elaboration, which is of 
equal likelihood. The law has been modified to accommo- 
date the noble gases. Numerous suggestions as to the 
places for the elements have been put forward, but until 
we arrive at something fairly definite, it is futile to discuss 
them in an elementary work. 

EXERCISES 

1. How much aluminum shoukl we theoretically obtain from 
an ore containing 90 per cent of bauxite ? 

2. Assume that " thermit " contains 75 per cent iron oxide ; 
how much of the mixture would be required to produce 6 lb. of 
metalHc iron? 

3. Suppose we had a barr of aluminum weighing 1800 g., how 
many cubic centimeters of water would it displace ? 

4. How much sodium would be necessary, assuming exact 
proportions, to produce 3 kg. of aluminum? 



134 



GENERAL INORGANIC CHEMISTRY 





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CHAPTER XXI 
GROUP IV. — CARBON-SILICON GROUP 

This group of elements possesses particular interest 
because, first, while the bridge-element, carbon, is the 
backbone of the living world, the type-element, silicon, 
occupies a similar position for the dead, or mineral world. 
Second, carbon occurs free, while none of the other ele- 
ments in this group has ever been found except combined 
with some other element. Third, while the type oxide is 
XO2, the bridge- and type-elements and the negative series 
also form XO. Fourth, while two members of the nega- 
tive series (tin and lead) have been known from early 
times, the third was predicted by Mendelejeff four decades 
ago and discovered in 1886. Fifth, the group contains 
thorium, the element with next to the highest atomic weight 
and one of the parent radio-active substances, 

Cai'bon has been studied. 

Silicon (from silex — flint), Si, at. wt. 28.4, is never found 
uncombined, although next to oxygen it is the most abun- 
dant element. It is found combined with oxygen, as silica 
(Si02), in the form of quartz, flint, agate, sand, or combined 
with oxygen and metals, as silicates, like mica, feldspar, 
and so forth. Its compounds constitute the basis of rocks 
and of the soil. 

It is prepared by the reduction of binary halogen or oxy- 
gen compounds by metals. This was the method used by 
Berzelius in 18 10. when he first separated it. It is also 

136 



CARBON-SILICON GROUP , 137 

prepared by heating the oxide mixed with carbon to very 
high temperatures in an electric furnace : — 

• Si02 + 2Cz^Si+ t 2 CO. 

Silicon is a dark brown, lustrous powder which does not 
conduct electricity. It is soluble in molten metals, like zinc, 
from which it crystallizes as black octahedra and needles ; 
sp. gr. 2.49. It is very hard and, fuses only at a white 
heat, when it may be run into molds. It is not soluble in 
ordinary single acids, but is in a mixture of hydrofluoric 
and nitric acids. It combines with the halogens and oxy- 
gen and sulphur when heated to from -f- 400° to + 600°. 
It combines with positive elements to form siHcides, and 
with carbon to form carborundum, SiC, when subjected to 
the temperature produced in an electric furnace. 

POSITIVE SERIES 

Titanmni occurs as oxide, rutile, perovskite (CaTiOg), 
m'enaccanite (FeTiOg). ZirconiiLin is found as zircon 
(ZrSiO^). Ceriiim occurs as cerite and in monazite. Tho- 
riitni occurs as silicate, thorite, and as phosphate in rare 
minerals. It is probably complex. 

They may be prepared by the method of Berzelius. 
Recently cerium has been , prepared by the Hall process 
for aluminum (Muthmann). 

They are all more or less dark, metallic, lustrous sub- 
stances which burn in oxygen or air to dioxides. The free 
metals are not used commercially. The alloys of titanium 
with iron are useful and the cerium alloy with iron (30 
per cent) gives brilliant sparks when filed (devil's touch- 
stone). 



138 GENERAL INORGANIC CHEMISTRY 

COiMPARISON OF PROPERTIES OF POSITIVE SERIES 



Element 


Titanium 


Zirconium 


Cerium 


Thorium 


Derivation of 
name . . . 


Titan — a 
deity 


Jargon (Z^rgiln) 


Asteroid 
Ceres 


Scandinavian 
god of thunder 


Symbol . . . 


Ti 


Zr 


Ce 


Th 


Discoverer . . 


Klaproth 


Klaproth 


Klaproth, and 
Berzeiius and 
Hisinger, in- 
dependently 


Berzelius 


Date .... 


1794 


1789 


1803 


1828 


Atomic weight 


48.1 


90.6 


140.2 


232.4 


Appearance 


Dark gray 
powder 


Glassy crystals 


Lustrous 
malleable metal 


Lustrous 
crystals 


Specific gravity 


3-54 


4-15 


7.04 


11.00 


Melting point . 


+ 2500° 


+ 1500° 


+ 623° 


Above + 2500° 



NEGATIVE SERIES 

Germanium was predicted by Mendelejeff, being called 
by him eka-silicon, and was discovered by Winkler in 1886 
in argyrodite, 3 (Ag2S), GeS2. * 

Tin, probably brought from the British Isles by the 
Phoenicians, was called plumbum candidum according to 
Pliny, but in the fourth century the word stannum, which 
first meant a mixture of metals, was applied to it. Tin 
occurs chiefly as the dioxide (Sn02, cassiterite), and is not 
widely distributed. It is found mainly in Malacca and 
Cornwall. The earliest known form of tin was in an alloy 
with copper, bronze. 



CARBON-SILICON GROUP I.39 

It is prepared by roasting to remove sulphur and arsenic 
combined with the other metals present and then heating 
the oxide with carbon : — 

Sn02 + 2C^Sn + t 2CO. 

As the ore usually contains some iron oxide, that and other 
metals are reduced at the same time and are present as 
impurities in the metal. They are removed by fusing the 
impure material at a low temperature, when the liquefied 
tin runs off and leaves the other metals behind. The 
process must be repeated several times. 

Ordinary tin is a silvery white, lustrous, crystalline, soft, 
malleable metal. Its crystalline condition is observed in 
one way by bending a bar of the metal. A cracking 
sound (*' tin cry ") is heard as a result of the friction of the 
crystals. They may also be observed by etching a bar of tin 
with hydrochloric acid, when remarkable striations appear, 
or depositing it electrolytically. It becomes brittle when 
heated to + 200°. It may be rolled into thin sheets (foil). 

Under suitable conditions of temperature (+ 20°), 
white tin changes into a gray powder. Other of its char- 
acteristic properties also change; for instance, the specific 
gravity changes from 7.3 to 5.8. This fact acquires serious 
importance when it is recognized that this '' tin disease " is 
contagious. Organ pipes made of tin may become utterly 
useless. The fact has been known since the time of 
Aristotle. The explanation is very recent. Ice changes 
definitely and quickly into water at zero. We may cool 
water below zero, but as soon as we disturb it, ice forms at 
once. Zero is the transition point of these two physical 
states. Twenty degrees is the transition point at which 
ordinary tin takes on its disguise or assumes its unstable 
allotropic form, for it changes back when the temperature 



140 GENERAL INORGANIC CHEMISTRY 

is elevated. The change to gray tin at +20° requires a 
long time and is not sudden, like the change of ice to water 
at 0°, or the change of selenium at -\- 200°. 

It does not tarnish or rust at ordinary temperatures, but 
burns, when heated in the air, with a brilliant Hght, form- 
ing Sn02. It combines directly with negative elements 
and dissolves in hydrochloric and sulphuric acids : 

Sn + 2HCli±:SnCl2 + tH2; 

and the alkalies : 

Sn + 2 KOH + H2O :± K2Sn03 + f 2 H2. 

It is oxidized by nitric acid and is not dissolved by it. In- 
directly SnO may be obtained. When chlorine is passed 
over the salt produced by the solution of tin in hydrochlo- 
ric acid, another chloride is formed : 

SnCl2 + CI2 1:^ SnCl4. 

It will thus be observed that the valence varies. It is 
bivalent and quadrivalent. When the metals form two 
classes of compounds with the electro-negative elements, 
the number of the latter is not only indicated by the Greek 
numerical prefix, as tin monoxide, dioxide, or tin dichlo- 
ride, tetrachloride, but also by variations in the ending of the 
name of the electro-positive element; for example, sta.nr\oiis 
oxide (SnO), st3.nno?^s chloride (SnC]2), and. stann/<; oxide 
(Sn02), and stannz'^; chloride (SnCl^). 

On account of its malleability, ductility, and unaltera- 
bility on exposure to air, tin is a valuable metal, and is ex- 
tensively used as block tin and in making tin-plate, which 
is essentially a thin sheet of iron covered with a film of 
tin. Tin is a constituent of important alloys, as brass, 
bronze, solder, bell metal, and so forth. 



CARBON-SILICOxN GROUP 141 

Lead \\di?> one of the earliest known metals. For a long 
while it was not clearly distinguished from tin. Pliny 
called \t phnnbmn nigrum to distinguish it ixo\\\ plumbum 
candidum. The Romans knew of lead and constructed 
waterways out of it. 

It occurs mainly as the sulphide (PbS, galena), carbon- 
ate (PbCOg, cerussite), chromate (PbCr04, crocoisite), and 
molybdate (PbMoO^, wulfenite). 

The preparation of lead illustrates the application of 
purely scientific facts to metallurgical economy. When 
lead sulphide is roasted, the oxide is formed : 

PbS + 3 0:r>PbO-f|S02. 

The oxide heated with carbon is reduced to the metal : 

PbO-f C^Pb + fCO. 

But as sulphur combines with oxygen, as shown in the 
first equation, the roasting is carried so far that only two 
thirds of the sulphide have been oxidized ; the furnace is 
then closed to shut out air, and the heat continued at an 
elevated temperature : 

PbS + 2 PbO:r> 3 Pb +f SO2. 

The cost of the carbon is saved and a part of the ore acts 
as the reducing agent. Lead is always impure when first 
prepared, as its ores carry variable amounts of gold and 
silver. The purification of lead may, therefore, be consid- 
ered more conveniently later. 

Lead is a soft, w^orkable metal, whose surface freshly ex- 
posed is bluish white and lustrous. It is not very strong. 
Its crystalline condition may be shown by etching with 
nitric acid or separation from its solutions by zinc (lead 
tree). 



142 



GENERAL INORGANIC CHEMISTRY 



While warm it is squeezed by hydraulic pressure into 
pipes used in plumbing and to cover electric cables. Lead, 
as usually seen, is dull gray. It readily tarnishes on expos- 
ure to the air, but the oxidation is superficial. When 
placed in pure water containing oxygen, it forms Pb(0H)2, 
which is soluble. If carbon dioxide is present also, the 
hydroxide is converted into a carbonate, which does not 
dissolve easily in the water. Hard waters bring about the 
formation of a coating of the carbonate and sulphate, 
which protects the lead from further corrosion. Lead is 

COMPARISON OF THE PROPERTIES OF THE 
NEGATIVE SERIES 



Element 


Germanu.'m 


Tin (Stannum) 


Lead (Plumbum) 


Derivation of name 


Germania 







Symbol .... 


Ge 


Sn 


Pb 

• 


Discoverer . . . 


Winkler 


Known in 
early times 


Known in 
early times 


Date 


1886 







Atomic weight . . 


72.5 


1 19.0 


207.1 


Appearance . . . 


Lustrous 


Lustrous 


Soft, lustrous 
metal 


Specific gravity . 


547 


7.29 


11-37 


Melting point . . 


+ 954° 


231-5 


322° 


Boiling point . . 





>i6oo° 


>i6oo° 



CARBON-SILICON GROUP 143 

insoluble in dilute hydrochloric and sulphuric acids, but is 
readily soluble in nitric acid. On account of its insolubility, 
sheet lead i^ extensively used in chemical works, especially 
in building sulphuric acid chambers. 

Lead in soluble forms is a cumulative poison, producing 
"lead colic," "wristdrop," and so forth, often observed in 
house painters. Lead forms the basis of a number of use- 
ful alloys, as type-metal, bird shot, solder, and so forth. 

EXERCISES 

1. If the temperature is regulated, PbS may be roasted in part 
to PbS04. Write the reaction showing the separation of lead by 
heating these two together. 

2. Iron when heated has a stronger attraction for sulphur than 
lead, bismuth, or anthnony. Write the reaction by which lead 
may be separated from galena when heated with scrap iron. This 
is a process also practised in the metallurgy of lead. 

3. Suppose the double chloride of cerium is CeCl4, 2 NaCl, write 
the reaction whereby the metal may be produced according to the 
method of BerzeUus. 



CHAPTER XXII 

GROUP II. — NEGATIVE SERIES: ZINC, CADMIUM, MER- 
CURY 

This series of elements is comprised of zinc, which was 
long used in its alloys (brass) before it was known ; cad- 
mium, a nearly constant impurity in zinc, which was dis- 
covered not a century ago; and mercury, the only liquid 
metal known, which was written about at least 300 B.C. 
All occur in nature as sulphides, mercuric sulphide (cin- 
nabar) doubtless attracting attention of peoples very early, 
as it is bright red. Mercury is the only member of the 
series found free in nature. The molecules of all of them 
at high temperatures contain only one atom. All form 
oxides of the type XO, while cadmium and mercury also 
form an oxide of the type XgO. 

Zinc was prepared during the Middle Ages. It oc- 
curs as the sulphide (ZnS, sphalerite or zinc blende, some 
of which is phosphorescent), carbonate (ZnCOg, cala- 
mine), silicate (Zn2Si04, willemite), and the complex oxide 
(Fe, Zn, Mn)0, (FeMn)203, franklinite. 

It is prepared by forming the oxide (if the ore is a 
sulphide, this is done by roasting) and then reducing with 
carbon in earthenware retorts at + 1300° to + 1400°. The 
vapor of zinc condenses to a liquid, which is cast into 
blocks called "spelter." 

It is a bluish white, lustrous metal which is crystalline. 
Its malleability varies with the temperature. Ordinarily it 
is brittle, but when heated to from + 100° to -1- 150°, it is 

144 



NEGATIVE SERIES: ZINC, CADMIUiM, MERCURY 145 

workable and can be rolled into sheets, hence it is rolled 
hot. At higher temperatures, just below the melting point, 
it is very brittle and readily pulverized. When zinc is 
distilled and the vapor suddenly cooled, a gray powder 
forms known as "zinc dust." It tarnishes in moist air, 
the tarnish forming a coat which is impervious. It decom- 
poses water only at red heat. At high temperature it 
unites with oxygen with an intense greenish white light, rich 
in actinic rays, forming zinc oxide. When pure it is slowly 
attacked by acids. As it is had in commerce it dissolves 
readily in acids and caustic alkalies, giving off hydrogen. 
Zinc dust is much more reactive than the massive form. 
The element in dissolving in the alkalies shows its electro- 
negative properties : 

Zn +2 NaOH::^Na2Zn02 + tH2. 

Zinc is used in sheet form for coating statues and in 
architectural adornment, in galvanic batteries, coating of 
iron (galvanized iron), and in the manufacture of several 
important alloys, as brass and argentan. 

Cadmium was discovered in some impure zinc carbonate. 
The smoke from zinc furnaces burns with a blue to green 
flame and deposits a white powder. When cadmium is 
present it is brown. It was thought to be arsenic at first, 
because it forms a yellow sulphide. Cadmia was an early 
name applied to zinc ore. 

It occurs chiefly with zincblende, as greenockite (CdS), 
and also in the carbonate. Some Silesian zinc ores 
carry 5 per cent, of cadmium. 

It is extracted in the same way that zinc is. It is the 
first portion of the distilled metal. 

Cadmium is a white, lustrous, fibrous metal which may 
be bent without a cracking noise. It is less easily soluble 



146 GENERAL INORGANIC CHEMISTRY 

in dilute acids than zinc. Zinc throws it out of solution. 
Cadmium is used chiefly in certain alloys which fuse at 
low temperatures. 

. Mercury distilled from cinnabar was known as hydrargy- 
rum (water silver). The earliest mention of argentitni 
vivum (quicksilver) was about 300 B.C. It is found some- 
times free in pockets, but chiefly as cinnabar (HgS), in 
California, Texas, Spain, and Austria. 
It is prepared by roasting in the air : 

HgS + 02^|Hg + fS02. 

Mercuric oxide, which we should suspect as being formed 
in the process, is decomposed at the temperature of the 
furnace. The essential factors in the metallurgy of mer- 
cury are ample cooling chambers to condense the vapor 
and provision for collecting the condensed liquid, which is 
readily absorbed by porous earthenware or bricks. 

It is the only positive element that is a liquid at ordinary 
temperatures. It is an excellent conductor of heat and 
electricity. It is opaque and has a brilliant silvery luster. 
The solid crystalHzes in regular octahedra. As ordinarily 
prepared, after straining through chamois skin, it contains 
small amounts of other metals. These are removed in 
part by treatment with various acids and then distilling 
under reduced pressure in contact with oxygen, which 
attacks such impurities as zinc. The oxides formed do not 
distill over (Hulett). When pure it is not affected by the 
atmosphere at ordinary temperatures. Just below the 
boiling point it forms the red oxide, HgO. It combines 
directly with chlorine, but is insoluble in dilute hydrochlo- 
ric and cold sulphuric acids ; it is soluble in dilute nitric 
acid. It dissolves almost all metals, especially gold, silver, 
tin, and sodium, forming amalgams. 



NEGATIVE SERIES: ZINQ CADMIUM, MERCURY 147 

On account of the wide range of temperature through 
which it remains Hquid, its low vapor tension and high 
specific gravity, mercury is used in some barometers. 
A column one square inch supported by the normal pres- 
sure of the air weighs about 15 pounds. If the column 
has an area of one square centimeter, it weighs about one 
kilogram. Its uniform expansion with changes of tem- 
perature makes it suitable for use in thermometers. Its 
amalgamating property is utilized in making mirrors, and 
in the extraction of gold and silver from their ores. 

Mercury forms two classes of compounds : bivalent, 
mercuric (HgO, HgC^, and univalent, mercurous (Hg20, 
^S2^h)- T^^ vapor of mercury is very poisonous, and so 
are its compounds. The metal in quantity is nearly in- 
soluble in animal secretions, so does not act as a poison^ 
unless in a fine state of subdivision. 



148 



GENERAL INORGANIC CHEMISTRY 



GROUP II. — Negative Series 



Element 


Zinc 


Cadmium 


Mercury 


Derivation of 
name .... 


German — zinn 
(tin) with Slavic 
suffix k. (Klugge) 


Cadmia 

fornicum 

(furnace zinc) 


Roman deity, 
Mercurius 


Symbol .... 


Zn 


Cd 


Hg 


Discoverer . . . 


Known in early 
times 


Hermann, Stro- 
meyer, indepen- 
dently (1817) 


Known very 
early 


Atomic weight 


65.4 


112.4 


200.0 


Physical state . 


Solid 


SoHd 


Liquid 


Appearance . . 


Bluish white, lus- 
trous metal 


White, lustrous 
metal 


Brilliant luster 


Specific gravity . 


7-1 


8.64 


13-55 


Melting point . . 


+ 419° 


+ 321° 


-39° 


Boiling point . 


+ 940° 


+ 800° 


+ 357° 



EXERCISES 



1. Write the equation for the roasting of zincblende ; also for 
the reduction of the oxide (ZnO) by carbon. 

2. Do the same for cadmium sulphide. 



CHAPTER XXIII 
GROUP I. — NEGATIVE SERIES: COPPER, SILVER, GOLD 

The members of this series possess great scientific and 
practical interest. All occur in nature in the free condi- 
tion and possess a characteristic brilliant luster. This prop- 
erty evidently attracted the attention of early peoples, for 
they were known to the ancients. All three also occur in 
sulphides, but with the exception of copper, not as oxides. 
They are soft, malleable, ductile, and the best known con- 
ductors of heat and electricity. Gold and silver are so soft 
that they are rarely used in the pure form, but as alloys. 
These alloys have served as mediums of exchange from 
the earliest days of bartering. The conversion of copper 
and silver into gold was one of the aims, if not the main 
ambition, that stimulated the alchemists. They are readily 
separated from their soluble compounds to the free con- 
dition by zinc, iron, and phosphorus. As they are little 
affected by the air, cooking (copper) and food vessels are 
made of their alloys. However, they are all poisonous in 
their soluble compounds. All combine directly with the 
halogens. Each forms two series of compounds, as illus- 
trated by their oxides: cuprous (CU2O), cupric (CuO); ar- 
gentous (Ag20), argentic (Ag202) ; aurous (AU2O), auric 
(AU2O3). 

Copper occurs not only as octahedral crystals in the Lake 

Superior region, but in important compounds, as cuprite 

(CU2O), chalcocite (CU2S), malachite [CuCOg, Cu(0H)2], 

azurite [2 CuCOg, Cu(OH)2], chalcopyrite (CU2S, Fe2S3), 

and bornite (3 CugS, FcgSg). 

149 



I50 GENERAL INORGANIC CHEMISTRY 

Silver occurs as argentite (Ag2S), proustite (AggAsSg), 
pyrargyrite (AggSbSg), argyrodite (3 Ag2S, GeS2), horn 
silver (AgCl), and in nearly all lead ores. 

Gold occurs, probably as the sulphide, along with cop- 
per and iron sulphide ('' sulphurets "), and as telluride, 
sylvanite [(Au, Ag)Te2]. 

Metallurgical practices involving the application of en- 
gineering skill and chemical principles are often quite com- 
plicated. The winning of these three elements from their 
ores depends upon the form in which they occur. As all 
three are often present in the ore of any one of them, we 
may consider their extraction together, and thus secure an 
excellent illustration of the intricate chemical relations 
involved in securing the metalhc elements on a commercial 
scale. 

First, if the metal is free : 

A. Copper is separated by crushing and washing the 
ore, then melting the metal out by heat, having added 
something {2, flux) to combine with the remaining country- 
rock to produce a slag, which is a liquid at the temperature 
when the metal is molten. The melted copper is heavier 
than the slag, sinks to the bottom of the furnace, is run 
off from time to time, and cast in molds. 

B. Silver and gold do not occur in sufficient quantity to 
be treated in this manner. They require some solvent to 
concentrate them. This solvent may form a simple or 
chemical solution. 

I. Simple solutions of silver and gold are produced by 
the direct treatment with mercury, which forms an amal- 
gam. Gravel containing free gold is a secondary forma- 
tion and is usually spoken of as "placer gold." If it 
contains enough gold to warrant its working, it is called 



NEGATIVE SERIES: COPPER, SILVER, GOLD i^i 

"pay dirt." The gravel is concentrated by pamimg, that 
is, it is shaken with a semi-circular jerk motion, similar to 
that employed in sifting meal or flour, to concentrate the 
heavy particles of the metals in the bottom of the '' pan," 
" cradles," or "tables" (the form and shape of the machine 
depending upon the amount to be treated, method of treat- 
ment, and materials at hand). The valueless rock above is 
then scraped, washed, or blown off. Mercury is added, and 
amalgamation of the silver and gold results. Gold, espe- 
cially, often occurs free in very small amounts, less than 
one part to the hundred thousand in quartz rock, which is 
worked on a large scale successfully for the extraction of its 
"values." This rock is usually hard and brittle. It is 
crushed under water in the presence of mercury by a 
method of stamping. The heavy mercury is washed free 
from any sand or dirt and the excess is squeezed out 
through chamois skin. The amalgam is then placed in an 
iron pot or retort and heated. The mixture of silver and 
gold remains behind. 

IL Gold is soluble in a water solution of chlorine, 
bromine, or an alkaline cyanide. When the crushed ore 
is treated with these liquids, the silver and gold form 
chemical solutions, which may be drawn off. On adding 
zinc, or iron, ferrous sulphate (FeSOJ, or hydrogen sul- 
phide, the silver and gold are precipitated from the clear 
solution as a brown or black mud. It is separated by 
filtering, and, when fused, assum.es the familiar metallic 
appearance. 

Second, when the metals occur in compounds, other 
procedures are followed. 

A. Preliminary treatment is necessary to put the metals 
in the free condition before the methods given above are 
applicable. Usually the ore is crushed and concentrated 



152 GENERAL INORGANIC CHEMISTRY 

in a current of water by shaking with various mechanical 
devices. The Hghter vahieless rock is washed away (" tail- 
ings "). The "concentrates" are roasted. Gold and 
silver are liberated. This material is then " amalgamated," 
"chlorinated," or "cyanided." 

B. However, when copper ore, which usually carries 
some gold and silver, is roasted, copper oxide is produced. 
To secure the copper, a smelting process is pursued. The 
ore, which nearly always contains some iron sulphide, is 
partially roasted. The iron sulphide is oxidized first, FeO 
being produced. Siliceous matter (sand) is added, the air 
shut off, and the temperature raised. The iron oxide com- 
bines with the silica, forming a fusible slag (FeSiOg) and 
floats upon the CuS, which melts and runs to the bottom 
of the furnace. The latter {matte, which contains some 
free copper) is run into another furnace, where, after it is 
two thirds roasted, the air is shut off and the reduction 
completed (see lead). This " coarse copper," which con- 
tains many impurities, as lead, arsenic, gold, silver, and 
so forth, is cast into ingots. 

The copper is then refined electrolytically. Thin sheets 
of copper joined to the negative pole of a direct current 
are suspended in a weak acid solution of copper sulphate. 
Slabs of the impure copper, weighing several hundred 
pounds, are suspended between the thin sheets and joined 
to the positive terminal. In the passage of the current of 
0.5 volt, or less, the copper travels from the positive to 
the negative pole, where it is deposited. Electrolytically 
refined copper is very pure. The impurities fall to the 
bottom of the tank, making a sludge which contains the 
gold and silver. 

C. Most lead ores, especially galena, carry some silver, 
which is found in the lead obtained. Often argentiferous 



NEGATIVE SERIES: COPPER, SILVER, GOLD 1 53 

and auriferous ores are purposely added to lead ores in 
the process of smelting. The molten lead passes through 
the mass, dissolving the gold and silver, and collects at the 
bottom of the furnace. It is cast into *'pigs" or run into 
iron pots. Molten zinc and lead are only slightly soluble 
in each other (less than 2 per cent). Silver is more soluble 
in molten zinc than in lead. When zinc is stirred in the 
molten lead obtained above, it dissolves the silver and floats 
on top. This solidifies at a temperature v^hen the lead re- 
mains a liquid and is skimmed off. The remaining lead is 
practically free from silver (Parkes process). 

The zinc-silver alloy contains some lead, which is finally 
removed by cupellation. In this operation, which consists 
in passing a blast of air over the molten metals in a cupel 
made of bone-ash, the lead is oxidized to litharge (PbO). 
This melts, some of it running over the edge of the cupel, 
and the rest is absorbed by the cupel. The zinc is then 
distilled off in clay retorts. 

Third, the gold and silver are separated by boiling in 
nitric acid, in which the latter only is soluble (quartation), 
or by electrolysis. The latter method is extensively used 
now in the following manner : The bar of mixed metals, 
connected with the positive terminal of an electric circuit, 
is suspended in an acid solution of silver nitrate and sep- 
arated by a heavy canvas partition from the negative 
terminal. The silver dissolves and is deposited in crystal- 
line form upon the negative plate, while the gold is col- 
lected as a brown mud by the canvas partition. The 
latter is burned, the metal fused and cast into bricks. In 
mints the gold is again refined by electrolysis in an acid 
auric chloride solution to remove platinum. 

The comparable properties of these elements are 
mentioned in the table. 



154 



GENERAL INORGANIC CHEMISTRY 
GROUP I. — Negative Series 



Element 


Copper (Cuprum) 


Silver (Argentum) 


Gold 

(Aurum) 


Derivation of 
name . . 


^s Cyprium 


Seolfor 


Ghel 

(be yellow) 


Symbol . . 


Cu 


Ag 


Au 


Atomic w^eight 


63.6 


107.88 


197.2 


Specific gravity 


8.93 


10.5 


19-3 


Appearance . 


Red 


White 


Yellow, 

lustrous 

metal . 


Crystalline form 


Octahedra 


Octahedra 


Octahedra 


Melting point . 


+ 1090° 


+ 960° 


+ 1060° 


Boiling point . 


+ 2100° 


+ 1360° 


+ 1800° 


Conduct with 
oxygen . . 


Tarnishes in moist 
air. If at high 
temperature, it 
burns with a 
green flame. 


Does not combine. 
Absorbs 22 vols, 
when melted ; 
when cooled 
gives it up with 
" sprouting " 


Not affected 


Soluble . . 


In nitric and 
hydrochloric acids 


Soluble in nitric 
acid 


Insoluble in 
single acids. 
Soluble in 
aqua regia, 
which liber- 
ates free 
chlorine 



NEGATIVE SERIES: COPPER, SILVER, GOLD 155 

Copper is not easily cast. In thin sheets it transmits 
green Hght. Its properties are much affected by impur- 
ities. A small fraction of a per cent of arsenic lowers 
its conducting power for electricity materially. It is ex- 
tensively used for this purpose. It forms many useful 
alloys, brass (with zinc) and Dutch metal (''gold leaf"), 
gun and bell metal (with tin), and bronze and german silver 
(with tin and zinc). 

Silver may be had in several allotropic forms in addition 
to the familiar insoluble variety : one that is soluble in 
water, giving it a characteristic blue color ; another giving 
a red solution. These are colloidal solutions {vide Chapter 
XXXVI). Such solutions of metals ordinarily insoluble 
in water, as silver, gold, and platinum, may be made by 
sparking wires underneath water. Silver may be obtained 
as a lilac precipitate, insoluble in water, and in a form 
which resembles gold in color and luster (Lea). Silver is 
oxidized by ozone. It turns black in contact with sulphur. 
This is commonly spoken of as " oxidized silver." Its 
alloys with copper are used for coinage purposes and for 
making silverware. 

Gold may be hammered into sheets so thin that it takes 
280,000 placed one upon the other to make an inch ("gold 
leaf"). It is so ductile that one gram may be drawn into 
a wire five miles long. Its alloys with copper and silver 
are used for coins and to make goldware. Pure gold or 
pure silver is too soft to be used alone for coinage pur- 
poses. Gold is commercially measured by carats, twenty- 
four being pure ; or by " fineness," one thousand being 
pure. 

EXERCISES 

I. Contrast the properties of the members of the positive and 
negative series of Group I. 



156 GENERAL INORGANIC CHEMISTRY 

2. How many ounces of gold per ton are represented by forty 
parts to the million? What would be the value of such ore, rating 
gold at ^20.00 per ounce ? 

3. Write the reactions taking place in roasting chalcopyrite, 
proustite, and sylvanite. Copper forms CuO ; arsenic, AS2O3 ; 
iron, FegOg ; and tellurium, Te02. 

4. Write the reaction by which copper sulphide (CuS) may 
reduce the partially roasted matte to produce metalhc copper. 

5. How does the law of partition apply to the Parkes process 
for the separation of silver from lead ? 



CnAt'tfiR XXIV 

POSITIVE SERIES OF GROUPS V, VI, VIl 

Group V. — Positive Series 

The three rare elements comprising this series, vana- 
dium, cokimbium, and tantalum, occur in rare complex 
minerals. While they are distinctly metallic in character, 
they are always found combined with oxygen in com- 
pounds, similar to the phosphates, which show acidic 
properties. For instance, the minerals are vanadates, 
Golumbates, and tantalates. 

Vanadium is found in the ashes of many plants, peats, 
and coals ; in fact, widely distributed, but in very small 
amounts. Its compounds have been found useful in dye- 
ing, making indelible ink, and ceramic decorating. Com- 
pounds of the other two have so far not exhibited proper- 
ties which make them useful. 

The elements may be prepared by the method of Ber- 
zelius or electrolysis of the fused double chlorides of the 
alkali metals. A recently devised method, the one now 
used, is very interesting. Some oxides, as magnesium 
oxide, when heated white hot, conduct an electric current 
(Nernst). These oxides break up into the metal and oxy- 
gen, but as they immediately reunite, no evidence of the 
dissociation is had after the current ceases to pass. If the 
oxides, in filament form, are treated in this manner in a 
vessel attached to a vacuum pump, the oxygen is drawn off 
and constantly removed by the pump. In time the fila- 
ment becomes one of the pure metal (von Bolton). In 

157 



58 



GENERAL INORGANIC CHEMISTRY 



this manner incandescent electric lamps are made contain- 
ing these elements as filaments. The "tantalum lamp" 
consumes about one half the current required by the car- 
bon filament, but in a no volt circuit, in order to get 22 
candle power, it is necessary to have a filament 50 centi- 
meters long. The filament is strung upon supporting- 
glass prongs and presents a spider web appearance inside 
the bulb. 

GROUP v. — Positive Series 



Element 


Vanadium 


COLUMBIUM 

(Niobium) 


Tantalum 


Derivation of 
name . . . 


The goddess 
Vanadis 


Columbia 

(Niobe, daughter 

of Tantalus) 


Mythological 
cliaracter, 
Tantalus 


Symbol . . . 


V 


Cb (Nb) 


Ta 


Discoverer. . 


Sefstrom 


Hatchett 


Ekeberg 


Date . . . 


1830 


1801 


1802 


Element 
isolated by . 


Roscoe (1867) 


Roscoe (1877) 


Berzelius (1824) 


Atomic weight 


51.2 


93.5 


181 


Appearance . 


Lustrous metal 


Grayish black 
powder 


White metal 


Specific gravity 


5-5 


7.06 


10.4 


Melting point . 


4- 1680° 


+ 1950° 


+ 2250° 



POSITIVE SERIES OF GROUPS V, VI, VII 159 

Tantalum in its purest form unites the hardness of the 
best steel with a greater toughness and ductility than is 
known to be possessed by any other metal. It is difficult 
to cut it with a diamond, not on account of its hardness, 
but because it is so tough. It is used in alloys to make 
small springs and anvils, the edges of which are subject 
to mechanical wear. 

Vanadium is utilized in alloys of iron, especially in the 
production of sheet and tool steel, and armor plates. It 
increases the malleability and hardness of steel after 
tempering. 

Group VI. — Positive Series 

The elements in this series differ from those of the neg- 
ative in never occurring free, but combined with oxygen and 
other elements. All may be prepared as crystalline leaf- 
lets by the Berzelius method, and in the massive form by the 
alumino-thermic process of Goldschmidt. They are hard, 
brilhantly histrous metals and are oxidized with difficulty 
at ordinary temperatures. When heated they combine 
with oxygen. All of them are used by alloying with iron to 
make high-grade crucible steels, which possess unusual 
strength, toughness, and hardness. They are fit for 
particular uses, especially in making high-speed cutting 
tools and small parts of machines that are subjected to 
serious shocks or constant vibration, as in automobiles. 

They exhibit very variable valence, as we shall see when 
we consider the halides and oxides. Uranium appears to 
be one of the original radio-active elements, which will be 
considered in the next chapter. 

Chromittni occurs as chrome-iron-stone, or ferrous chro- 
mite [FeO(Cr203)], and as crocoisite (PbCrO^). 



l6o GENERAL INORGANIC CHEMISTRY 

Chromium is converted into many compounds which 
are used for the preparation of colors, battery fluids, pho- 
tographic materials, and so forth. Chromium dissolves in 
hydrochloric acid. When previously dipped in nitric acid, 
it becomes *' passive " and no longer displaces hydrogen 
in hydrochloric acid. 

Molybdenum occurs mainly as sulphide (MoSg) and as 
wulfenite (PbMo04). 

Molybdenum in the form of compounds is used in the 
laboratory. The metal, when melted, dissolves carbon and 
becomes so hard that it will scratch glass. 

Tungsten occurs as wolframite (FeWO^), scheehte 
(CaWO^), and stolzite (PbWO^). 

Tungsten is used for making filaments for incandescent 
electric lights. *' Tungsten lamps " yield the same amount 
of light as those with carbon filaments, but use only one 
quarter to a third of the current. They have a longer Hfe, 
but have not been made commercially so that they may be 
used at all angles and to withstand the constant vibration 
of cars, and so forth. Its compounds are used in dyeing 
and to render cloth fireproof. 

Uranium occurs as uraninite (UgOg, or UO2, 2 UO3), 
and in all radio-active minerals. The latter are very com- 
plex in composition. It has the highest atomic weight 
of any of the accepted elements. 

The compounds of uranium are used in dyeing and in 
making "uranium glass," which shows a yellowish green 
fluorescence, especially under the influence of ultra-violet 
light. 



POSITIVE SERIES OF GROUPS V, VI, VII 161 

GROUP VI. — Positive Series 



Element , 


Chromium 


Molybdenum 


Tungsten 
(Wolframium) 


Uranium 


Derivation-of 
name. . . 


XpCjfxa (color) 


MoAv/36o? (lead-like 
appearing minerals) 


Tung (heavy) 
+ sten (stone) 


Planet 
Uranus 


Symbol . . . 


Cr 


Mo 


W 


u 


Discoverer 


Vauquelin and 

Klaproth 
independently 


Scheele (Hjelm 
isolated metal, 1782) 


Scheele 

(d' Elhujar 

1783) 


Klaproth 
(Peligot 
isolated ele- 
ment, 1842) 


Date . . . 


1797 


1778 


1781 


1789 


Atomic weight 


52.1 


96.0 


184.0 


238.5 


Specific gravity 


6.7 


8.6 


19.1 


18.7 



Group VII. — Positive Series 

Only one element is known in this series : — 
Manganese, Mn, at. wt. 55, which was discovered by 
Bergmann (1774) and isolated by Gahn, occupies a unique 
position. In general physical properties it shows little or 
no resemblance, but certain characteristics of its com- 
pounds carry out the analogy, to the group type, chlorine. 
It forms no compounds with hydrogen, but several with 
oxygen. It bears a close resemblance in physical proper- 
ties to iron in Group VIII. 

Although small amounts of metallic manganese are 
found in meteorites, the element is found chiefly as the 
oxygen compounds and always contaminated with iron. 
The main occurrence of manganese is as pyrolusite (Mn02), 
hausmannite (Mn304), braunite (3 Mn203, MnSiOg), man- 
ganite (Mn203, H2O), and rhodochrosite (MnCOg). 



l62 GENERAL INORGANIC CHEMISTRY 

It is prepared by reducing the oxide with carbon, as 
iron is, and by the Goldschmidt process. 

It is a hard, white, malleable metal which fuses at 
+ 1900° and has a specific gravity of 'j.2 to 8. It oxidizes 
very easily, " rusting " in moist air, and is readily soluble in 
acids. It forms a number of different salts divided into 
five different classes. In none of these is it univalent as 
are the other members of this group. It forms alloys with 
iron (20 to 80 per cent), ferromanganese, for example, 
which dissolve a large percentage of carbon and play an 
important part in the metallurgy of iron and steel. 

EXERCISES 

1. Write equations indicating the reduction of the following 
compounds by the alumino-thermic reaction : — 

Cr,03, V2O5, U3O,, Uxv,0,, 

2. From what has been learned, are you able to predict another 
member of the positive series of Group VII ? If so, tell some of 
its properties. 

3. Write the equations for the preparation, by the method of 
Berzelius, of the metals from the following halides : — 

WCI2, UClg, and MnCls. 



CHAPTER XXV 

RADIUM AND RADIO-ACTIVE PHENOMENA 

PJienomenon of Radio-activity. In 1896 Becquerel ob" 
served that compounds of uranium yield a radiation which 
affects a photographic plate through light-proof paper 
(Becquerel rays) in a way somewhat similar to the X-rays. 
Schmidt learned, that thorium compounds do the same. 
These two elements have the highest known atomic 
weights. An electroscope, when well insulated, will re- 
tain an electric charge for a long time. It is instantly 
discharged when exposed to the X-rays. The air is said 
to be "ionized" and becomes a conductor of electricity, 
like a copper wire. If a small amount, a fraction of a 
gram, of any uranium or thorium compound is brought 
near a charged electroscope, it is discharged also, but at 
a slow rate, which varies with the charge, amount of sub- 
stance, distance from the instrument, and so forth. By 
making all the factors fixed, except the kind of compound 
used, and timing the rates of discharge for different com- 
pounds, we secure a method of quantitatively measuring 
the "radio-activity." This term was applied by Madame 
Curie to the phenomenon discovered by Becquerel. She 
proved that the radio-activity of pure uranium salts varied 
directly according to the percentage of that element 
present. Some of the uranium ores, however, were found 
to be four or five times as active as that compound of ura- 
nium with the highest percentage of uranium. The same 
was true for thorium. Therefore, that something more 

163 



164 GENERAL INORGANIC CHEMISTRY 

active than either of these must be present, in the natural 
compounds, was the postulate which led her and her hus- 
band to the separation of salts of radiitm. 

The ores in which radium occurs most abundantly, 
pitchblende, uraninite, and carnotite, are very complicated 
compounds of uranium, thorium, and other rare elements. 
The radium occurs in them in extremely minute amounts. 
During the elaborate chemical treatment for the extrac- 
tion of the uranium and concentration of the radium, the 
course followed by the latter is readily ascertained by 
determining the ionizing value of the various products 
obtained in the process. 

Concentration of Radium Compoimds. The ore is pulverized, 
digested in boiling sulphuric acid, diluted, and filtered. Most of 
the uranium goes into solution, the radium remaining in the 
residues. We do not know the compound in which radium 
occurs in its ores, but this conduct indicates that it exists either 
in a form insoluble in sulphuric acid, or in a form which combines 
with the sulphuric acid to produce an insoluble sulphate. We 
know that radium forms an insoluble compound with sulphuric 
acid. The residues are then fused with sodium carbonate and 
leached with water. This is the common method for decompos- 
ing insoluble sulphates. The sodium sulphate produced in the 
fusion is dissolved by the water. The residue, carbonates insolu- 
ble in water, is then treated with hydrochloric acid, as the car- 
bonates are decomposed and dissolved by that acid. Sulphuric 
acid is added to separate the alkaline-earth metals. Barium 
sulphate (BaS04) is very insoluble in water, and the final solution 
is made in hydrobromic acid. Radium bromide is less soluble 
in water than the corresponding compound^ of barium. They 
are separated by fi-actional crystallization.* 

* When a solution containing two solutes is evaporated until crystallization 
begins, the excess above saturation of both solutes separates cjut. As the 
solution tension of different solids are as a rule unlike, one solute separates 



RADIUM AND RADIO-ACTIVE PHENOMENA 165 

Properties of Radium Compounds. Radium is known 
only in its compounds, the bromide, chloride, sulphate, 
acetate, and carbonate. Weak alloys of radium with mer- 
cury have been made, but little is known of them. When 
freshly prepared, the salts of radium are white and resem- 
ble similar salts of barium. In time, however, they become 
purple and brown. Radium shows an equivalence of 1 13.25 
to 35.45 of chlorine. Chemically it resembles barium, 
which is bivalent, therefore it has an atomic weight of 
226.5 (Curie, Thorpe). It possesses a characteristic spec- 
trum, hence it is regarded as an element (7'/^^ Chapter II). 

We are more familiar with the conduct of radium bro- 
mide (RaBr2) and chloride (RaCl2) than the other salts. 
They show remarkable photo-activity and intense ioniz- 
iiig power. The purest bromide shows an activity about 
1,800,000 times that of uranium. These compounds con- 
stantly evolve heat, and in relatively enormous quantities. 
For instance, i g. evolves 100 calories per hour. The 
total amount of heat that may be spontaneously produced 
by I g. has been estimated to be nearly 100 billion calories, 
or equivalent to that produced by burning over 300 kg. 
of hydrogen in oxygen. The temperature of sohd radium 
bromide is from 1° to 5° higher than the surrounding media 
from — 190° to + 450°. 

Radium salts are phosphorescent. When in contact 
with, or near by, certain minerals and chemical compounds, 
as diamonds, willemite (zinc ortho-silicate), Sidot's blende 
(zinc sulphide), and barium platino-cyanide, this phenome- 

in greater amount, but it is always contaminated by some of the other. If a 
solution be made of this mixture and crystallized, a solid is obtained with a 
still larger proportion of that one which preponderated. By repeating the 
process a number of times, a very pure solid is obtained at one extreme and 
a very pure liquid at the other, but each contains some of the other. This 
process of fractional crystallization is one extensively practiced in chemistry. 



l66 GENERAL INORGANIC CHEMISTRY 

non is most pronounced. Radium salts darken paper when 
in contact with it for some time ; and give some glass a pink 
and other a brown color, depending upon the composition 
of the glass. Radium compounds exert physiological 
actions not yet thoroughly understood. It interferes with 
the germination of seed and retards the growth of plants. 
In contact with living flesh, even when confined in glass 
tubes, it produces acute irritation, which often results in 
bad sores difficult to heal. It has a destructive action upon 
some animal cells and stimulates others. It has been used 
successfully, by contact action, in the treatment of some 
forms of disease, as lupus and goitre. 

Explanation of the Co7iduct of Radio-active Substajtces. 
The most acceptable explanation by which these unusual 
and unique properties are understood depends upon the 
assumption that the rays emitted by radio-active compounds 
consist of minute particles of two kinds. Those particles 
which produce the ionization effects are known as a-parti- 
cles. They bear a charge of positive electricity, and have 
twice the mass of a hydrogen atom. Those particles which 
produce the photographic effects are called the ^-particles. 
They bear a charge of negative electricity and are only 
about o.ooi the mass of a hydrogen atom (electrons, cor- 
puscles). If these are screened off, by methods too com- 
plicated to explain here, rays are still obtained, ^-rays, 
which resemble the X-rays in penetrating and ionizing 
properties and photo-chemical effects. The 7-rays have 
not been found except when y8-particles were present. 

Emanation. Radium constantly produces a gaseous 
substance condensable at — 150°, known as radinin emana- 
tion (Rutherford). The amount produced is increased 
by heating or dissolving the soluble salts in water. The 
emanation is far more radio-active than radium, It is 



RADIUM AND RADIO-ACTIVE PHENOMENA 167 

not a permanent body, but disintegrates quite readily, 
losing one half its activity within four days. As the 
emanation decays, a series of other radio-active bodies is 
produced, each disintegrating at a characteristic rate. 
Each gives off a-particles, or /3-particles and 7-rays, or 
both, and two of the series give none of these. The 
emanation, having expended its energy, as it were, event- 
ually changes, in part at least, into the final inactive ele- 
ment, heHum. (Ramsay, Soddy.) 

Life History of RadiiLin. As the radium is disintegrat- 
ing and it eventually disappears, we must account for its 
presence in the minerals from which it is extracted. Every 
uranium mineral contains radium and the emanation in 
proportion to the amount of uranium present. When a 
uranium compound is freed from radium, the emanation is 
slowly but regularly reformed. Therefore, it appears 
that uranium is the source. If we express the life of each 
educt in terms of the times required to decay to half value, 
the history of radium may be shown by a diagram as 
follows (Rutherford) : 

U — > U-X -> Ionium -> Ra — > Emanation ~> A ^ 

5X io9 yr. 22 da. ? 2000 yr. 3.8 da. 3 min. 

B-^C-^D^E-^F^G 

26 min. 19 min. 40 yr. 6 da. 45 da. 140 da. 

The same, but not so completely, may be shown for 
thorium. A number of radio-active substances have been 
announced, as polonium, actinium, emanium, radio-lead, 
and so forth. Most of these have been accounted for as 
containing an excess of one or several of the disintegration 
products shown above, or in a similar diagram for thorium. 

Recently Ramsay has shown that when the emanation 
decays in the presence of water alone, neon and not helium 



l68 GENERAL INORGANIC CHEMISTRY 

is produced. If the decay occurs in the presence of 
water containing a copper salt in sohition, argon is pro- 
duced. Therefore it appears that radium emanation, the 
most active substance known, disintegrates into one mem- 
ber of the family of inert gases, helium, neon, or argon, de- 
pending upon conditions. So far efforts to convert argon, 
neon, and helium, obtained from other sources, into each 
other have not been successful. Yet the transmutation of 
one element into another appears to have been accom- 
plished. 

EXERCISE 

Harmonize the last sentence with the definitions of an atom 
and an element. 



CHAPTER XXVI 

GROUP VIII. — THE IRON METALS 

The elements arrange themselves in the eighth group 
in quite a different manner from that observed in the other 
groups. They form four periods of three elements each. 
In each period the elements have nearly the same atomic 
weight, the extremes not differing by more than five units. 
When arranged in the order of the increase in atomic 
weight, three vertical series are obtained. The members 
of each show striking similarity in their chemical conduct. 
This is not true in one case ; namely, with nickel and cobalt. 
Their positions in the table are reversed. This constitutes 
an exception to the law, as all efforts so far to show a differ- 
ent relationship in their atomic weights have been in vain. 
The members of each period resemble each other in 
physical properties to a marked degree. We do not know 
enough about the gadolinite metals (samarium, europium, 
and gadolinium) to say definitely that they belong in this 
group, but from the atomic values, if the law is true in the 
main principle, they are properly placed in the table. The 
members of the first vertical series, iron, ruthenium, and 
osmium, are readily oxidized, whereas the others are not. 
In fact, many of their compounds yield the free elements on 
heating in the air. 

THE IRON METALS 

Iron, cobalt, and nickel are brilliant, lustrous, malleable, 
ductile metals which conduct heat and electricity. They 
possess properties, strength, unalterability on exposure to 

169 



I/O GENERAL INORGANIC CHEMISTRY 

the air, and so forth, that make them of great commercial 
importance, while the chemistry of the three metals is of 
extreme interest. Iron alloyed with certain other metals 
(as nickel, molybdenum, and tungsten) acquires unusual 
properties of strength. 

If we may draw distinctions among the elements, iron is 
the most imiportant among the metals, and is widely dis- 
tributed in nature. Fine grains of free iron are found in 
the coal measures of Missouri, some basalts, and on the 
Island of Disko. Meteorites, visitants from otherwhere, 
are primarily metallic iron with from 3 to 8 per cent of 
metallic nickel. The presence of the latter element dis- 
tinguishes it from that of terrestrial origin. The chief 
occurrences, from which the metal is extracted, however, 
are the oxides : magnetite (FcgO^), hematite (Fe203), 
limonite (brown hematite, 2 FcgOg, 3 H2O), siderite (black 
band ore, FeCOg). It occurs also as sulphides, especially 
as disulphide (pyrites, FeSg), which is an ore of sulphur. 
It is found in many silicates and is present as an impurity 
in almost all rocks. Its compounds constitute the coloring 
matter of most soils, vegetation, and blood of animals. 

Cobalt and Nickel occur chiefly as the sulphides and 
arsenides : smaltite (C0AS2), cobaltite (CoAs2,CoS2), nic- 
colite (NiAs), gersdorffite (NiS2, NiAs2), pentlandite 
[(Ni, Fe)S] ; and in certain silicates (garnierite) and 
other minerals, especially nickeliferous pyrrhotite. 

Pure iron js prepared as a powder by heating especially 
purified iron oxide, or oxalate (which gives an oxide on heat- 
ing), in a stream of hydrogen at a temperature of -f 600° : 

Fe203 + 3 H2 ^ 2 Fe + 3 H2O. 

This dark powder, if the reduction is made at a red heat, 
glows on exposure to the air and burns (pyrophoric). It 



THE IRON METALS 171 

melts transitionally at + 1900° ; and is a tolerably soft, tough 
metal, which may be magnetized. It may be drawn into 
wire through diamond dies. It rusts in moist air. Boiling 
water is decomposed by finely divided iron with the evolu- 
tion of hydrogen. Chemically pure iron is rarely seen, 
although the best iron piano wire contains 99.85 per cent 
of the metal. 

Technical iron is continuously produced on an enormous 
scale by smelting the ore in large blast furnaces, some 
yielding a thousand tons a day. The chemistry of iron 
and the principles involved in its extraction from its ores 
fill large volumes. The reactions involved are compli- 
cated. For our purposes a simplified statement will 
suffice. 

. Iron ore is essentially an oxide. It is reduced to the 
metallic form by heating with carbon. Coke or charcoal 
is used, not only for this purpose, but to produce the 
necessary heat by burning. The ore always contains many 
impurities, mainly siliceous (sandy) in nature. Siliceous 
matter when heated with lime forms a glass (slag) fusible 
at the temperature of reduction of the iron oxides. Lime- 
stone on heating yields lime, so the stone is added to 
"flux " away the silica. If the rocky impurities are mainly 
basic, that is, limestone, then sand is added to flux them. 

A blast furnace is essentially a circular structure, made 
up of two truncated cones, the bases of the elongated 
one resting upon the base of the other, with a shell of 
metal. It is lined with a heat-resisting material, like fire 
brick. They are sometimes 40 m. high and 12 m. in 
diameter at the widest part. The top is closed by a bell 
which descends when a charge is added. The furnace 
rests upon a sandstone basin (hearth) which must be well 
drained. At the lowest point in the hearth is an opening 



1/2 GENERAL INORGANIC CHEMISTRY 

for running off the molten metal. Air blasts (tuyeres) are 
provided at the proper height above the hearth. Between 
the metal outlet and the air inlets is another, but smaller, 
opening through which the molten slag runs out continu- 
ously during the operation of the furnace. Coke, iron 
ore, and limestone (solids) are dumped in at the top. The 
last two constitute the " burden " of the charge. Air is 
driven in through the tuyeres. The carbon burns : 
CH-02^:C02, which, coming in contact with more hot 
carbon, is reduced: C02 + C;^2CO. The monoxide 
thus produced, on coming in contact with iron oxide, re- 
duces it : 

Fe203 + 3 CO ^ 2 Fe + t 3 CO2, 
or FcgO^ + 4C0^3Fe + J4 CO2. 

The carbon dioxide passes up and out of the top of the 
furnace. The reaction is reversible, so an excess of CO is 
necessary. Pure iron does not melt at the temperature it 
is produced (+ 500° to +900°). It dissolves carbon, how- 
ever. This it secures in part from the carbon monoxide : — 

Fe + .r CO :;!: FeC;r + ;irO. 

Iron which has dissolved carbon (2 to 6 per cent) melts at 
+ 1050° to + 1250°; hence it immediately falls as drops 
to the hearth of the furnace, where it is tapped every six 
hours, run into molds of sand (cast into "pigs"), and is 
known as cast iron. The oxygen combines at once with 
more carbon. The lime (CaO) combines with the silica 
(5102) to make the slag (CaSiOg). The blast may be cold 
or hot; in the latter event, the waste hot gases are passed 
through " stoves " which serve to heat the air before it 
enters through the tuyeres. Thus it will be seen that soHds 
enter the top, and air enters the bottom. Gases are dis- 
charged from the top, and liquids drawn from the bottom. 



THE IRON METALS 173 

The whole process is carefully controlled by analyses 
of the materials entering and products obtained. The 
barometric pressure and humidity of the air are also con- 
stantly noted. 

Commercial iron always contains more or less carbon, 
which may be in the form of free graphite or combined 
with the iron. The presence of combined carbon (FegC) is 
shown when iron is dissolved in hydrochloric acid by the 
hydrocarbons in the hydrogen evolved. Part of the odor 
of these gases is due to hydrogen compounds with the 
small amount of sulphur and phosphorus always present 
as impurities. There are three classes of commercial iron : 
(a) Cast iro7i, containing 2 to 6 per cent of carbon. It is 
brittle, but very hard ; can be cast, but not welded, and can 
be made temporarily magnetic. Cast iron may be white, 
when practically all the carbon is in the combined condi- 
tion. This is produced when it is chilled from the liquid 
state so suddenly that the carbon has no time to separate 
out. It is a solid solution of FcgC in iron. It may be 
gray, when all or most of the carbon is in the graphitic 
form. This results when time has been allowed in the 
cooHng for the crystallization of the carbon. Cast iron 
also contains silicon, sometimes as much as the carbon 
present, a little manganese, and less sulphur and phos- 
phorus. 

(^) When cast iron is melted and the carbon burned 
away until there is less than 0.5 per cent, ivronght iron is 
produced. This is accomplished by running molten cast 
iron, or melting pig iron, on to iron oxide mixed with a 
little lime in a reverberatory furnace. The mixture is 
stirred with iron rods (" puddled "). The carbon is burned 
out and escapes as monoxide ; the silicon is oxidized to 
silica (5102) and fluxes with the lime. As the iron becomes 



1/4 GENERAL INORGANIC CHEMISTRY 

purer, it stiffens. It is removed in balls (''blooms"), and 
freed from the slag by rolling and hammering. Powerful 
machines do this work. Wrought iron is very tough, but 
comparatively soft; it fuses at + 1600°, or higher, accord- 
ing to its purity. It cannot be cast, but is easily worked 
with the hammer and welded when hot (4- 1000°), and is 
much stronger than cast iron. 

(c) Bessemer sought to make wrought iron by bubbling 
air through molten cast iron to burn out the carbon, and 
failed. When the carbon was nearly burned out, the iron 
was no longer a liquid and consequently could not be 
^poured from the vessel. After tragic experiences, he 
decided to stop the process at a point when the metal 
remained sufficiently liquid to be easily transferred. He 
thus discovered how to make steel on a tremendous scale 
(1856), although steel had been known for a long time. 
Steel contains from 0.5 to 2 per cent of carbon and 
possesses the advantageous properties of both cast and 
wrought iron. It is usually hard and possesses great 
strength. It can be made permanently magnetic. It may 
be cast and welded. If hot steel is suddenly cooled by 
plunging into water, it becomes very hard and compara- 
tively brittle. If it is reheated and cooled to a definite 
temperature, desirable variations in hardness may be ob- 
tained. This is known as "tempering." If it is slowly 
cooled, it is tolerably soft and tough. This is known as 
"annealing." These are often combined by quickly chill- 
ing the exterior, which becomes hard, and then cooling 
the interior slowly, which makes it tough. 

The manufacture of steel, an immense industry, as the 
uses of iron are widespread and important, is essentially 
dependent upon two processes ; namely, the Bessemer 
("pneumatic") and the Siemens-Martin ("open-hearth"). 



THE IRON METALS 175 

In the former, melted cast iron is run into a *' converter " 
(an egg-shaped vessel lined with fire-resisting material) and 
air bubbled through it from the bottom. A very high tem- 
perature, sufficient to melt wrought iron with its highest 
percentage of carbon, is produced by the oxidation of the 
carbon, silicon, manganese, and some of the iron. Enough 
ferromanganese (which contains a large percentage of car- 
bon) or coke is added to reduce the oxidized iron and give 
sufficient carbon to make the mass fusible. It is then 
poured off and cast into steel ingots. The Open-hearth 
process applies the principles involved in a different way. 
The cast iron is melted by playing a gas-fuel flame, an 
exaggerated blowpipe, as it were, in a dish-shaped furnace, 
lined with sand. Scrap iron and iron oxide are added in 
proper amounts. The heat is continued eight or ten hours, 
or until a test sample shows that the process is complete. 
The liquid steel is then drawn off and cast into ingots. 

The two great enemies of steel are phosphorus and sul- 
phur. The former makes it "cold short" and the latter 
** red short" ; that is, the presence of those two elements, 
even in fractions of a per cent, makes steel brittle, when it 
is cold or hot, respectively. In the two processes referred 
to, the lining of the converter or hearth was siliceous or 
acidic, which facilitated the removal of sulphur. To re- 
move phosphorus, the lining is made with a preponderance 
of alkaline earth metallic oxides (calcium and magnesium) 
and then the processes are known as " Basic Bessemer " or 
"Basic Open-hearth." 

Iron as an electro-positive element gives two classes of 
salts: ferrous (bivalent, FeO) and ferric (trivalent, Fe203); 
as a negative element, the ferrates (FeOg). Iron is readily 
soluble in acids. Galvanized iron or tin plate is made by 
rolling iron into thin sheets or pipes, treating with acids to 



176 



GENERAL INORGANIC CHEMISTRY 



remove any rust (oxide) that may have been produced and 
to give a perfectly clean metallic surface ('* pickling "), and 
then passing it through molten zinc or tin, which forms a 
thin coating on the iron. When placed in a solution of a 
copper salt, iron becomes coated with copper. If the iron 
is previously dipped into concentrated nitric acid, washed, 
and then dipped into the copper solution and removed, no 
copper is deposited. On jarring the iron, copper at once 
separates from the adhering solution. The iron is said to 
have assumed the ** passive " state. This condition may 
also be brought about by dipping iron into a solution of a 
dichromate (K2Cr207, for example). Iron so treated 
remains exposed to the air and moisture a long time with- 
out any indication of rusting. 

It is difficult to extract nickel and cobalt from the ores, 
as it is hard to separate them not only from the other 
metals but also from each other. When they are had in 



Element 


Iron 


Nickel 


Cobalt 


Derivation of 
name . 


Iren (Is, ice) 


Kopparnickel 
(Kupfer-nickel) 


Kobold (an evil 
spirit) 


Symbol . . . 


Fe- 


Ni_ 


Co 


Discoverer . . 


Known to 
ancients 


Cronstedt 


Brandt 


Date . . . 





1750 


. 1735 


Atomic weight 


55-9 


58.7 


59.0 


Appearance 


Silvery white 


Bluish white 


Pinkish white 


Specific gravity 


7.8 


8.9 


8.5 


Melting point 


+ i55o°to + i8oo° 


+ i30o°to + i6oo° 


+ 1500° to f 1800° 



THE IRON METALS 1 77 

the form of the oxides they may be reduced with carbon : 
NiO + Cr^Ni + CO; or by hydrogen : CoO + H2:r^Co + 
H2O. Nickel is separated from cobalt by means of carbon 
monoxide (Chapter XV). 

While iron oxidizes most readily in moist air, or when 
heated in oxygen, cobalt and nickel resist the action of 
oxygen at ordinary temperatures, and are consequently 
used in plating, as in nickel plate. Nickel and cobalt plat- 
ing — for the latter serves quite as well as the former — 
is accomplished by making an iron object the negative pole 
in water containing a soluble salt of nickel or cobalt, 
usually a cyanide. It is subsequently burnished. At high 
temperatures they oxidize more easily. 

EXERCISES 

1. Why is it necessary to have the ground upon which the 
hearth of a blast furnace rests well drained? 

2. Why is it desirable to note the barometer and know the 
humidity of the air in operating a blast furnace? 

3. In using "sheet tin" the presence of cracks in the tin is to 
be avoided. Why? 



CHAPTER XXVII 

THE PLATINUM METALS 

The platinum metals may be conveniently considered as 
light and heavy. The latter have atomic values and spe- 
cific gravities nearly twice the former. As a rule, they 
occur native in small metalUc grains in certain sands, which 
may carry more or less gold, especially in the Ural Moun- 
tains, Sumatra, Australia, and California. The alluvial 
sands are washed as in ** placer " gold mining. The lus- 
trous particles thus obtained usually contain from 50 to 60 
parts of platinum, 2 of palladium, 7 iridium, 1 5 ruthenium, 
besides gold, and copper and iron compounds. The sepa- 
ration of these different metals is a difficult and tedious 
process. Platinum is obtained also from an arsenide (PtAsg, 
sperryhte) found in Canada. Palladium is found in Brazil 
alloyed with gold, and in some selenium ores. It also 
occurs in some nickel ores (pyrrhotite) in quantities too 
small to be detected by the ordinary methods of chemical 
analysis, and accumulates in the slimes during the purifi- 
cation of large quantities of the extracted nickel. 

THE LIGHT PLATINUM METALS 

Riithenmm is steel-gray, very hard and brittle. 

Rhodium is very insoluble, not being attacked by aqua 
regia. It is hard and difficult to fuse. When alloyed with 
iridium and platinum, a material is had that is very resistant 
to the action of chemicals, especially acids. 

Palladium is a silvery white metal, which, when finely 
divided, dissolves in hydrochloric, sulphuric, and nitric 
acids. Ignited in the air it becomes dull by oxidation, but 

178 



THE PLATINUiM METALS 1 79 

on raising the temperature it reassumes a metallic appear- 
ance. Sheet palladium absorbs, when freshly ignited, 370 
volumes of hydrogen gas at ordinary temperatures, and 650 
volumes at + 90° to + 100°. Palladium, when used as 
negative electrode in the decomposition of water, will 
absorb 960 times its volume of hydrogen. This would 
indicate the compound Pd4H2, or Pd2H, but the amount 
of occluded hydrogen may be caused to vary with 
increase of pressure; that is, concentration. Therefore, 
the absorption of the gas by the metal appears to be a 
case of "sohd solution." Hydrogen absorbed by palla- 
dium is more reactive than the free gas. It will precipi- 
tate copper, which is less electro-positive than hydrogen, 
from its salts. Free hydrogen does not do it. " Palladium 
sponge," made by igniting a salt, which has absorbed 
hydrogen, sometimes becomes heated in the air as a result 
of oxidation of the hydrogen to water. *' Palladium black," 
that is, finely divided palladium, will absorb 980 volumes of 
hydrogen. On introducing a sheet, or sponge, of palladium 
into the flame of an alcohol lamp, it is covered with soot, 
due to the hydrogen being withdrawn from the hydrocar- 
bons. Palladium is not used extensively in the arts. 

THE HEAVY PLATINUM METALS 

Osmitim is the heaviest known substance. It does not 
fuse even at the temperature of the oxyhydrogen flame ; 
it only sinters at about + 2500°. While it is very difficult 
to fuse, it is the most easily oxidized of the platinum metals. 
In fine powder it burns when ignited in the air to OSO4. 
Incandescent lamps have been made with filaments of me- 
tallic osmium. The lack of a sufficient amount of its ores 
has prevented any extensive use of these lamps. 

Iridium is similar in properties to rhodium, being very 



l80 GENERAL INORGANIC CHEMISTRY 

difficult to fuse. When alloyed with platinum it renders 
it quite hard. 

Platinum is a soft but very tough and malleable metal 
which may be drawn into fine wire and hammered into 
foil. Below its fusing point it softens and may be welded. 
When it is fused it absorbs oxygen and gives it up on cool- 
ing, like silver. At ordinary temperatures platinum black 
absorbs 3 10 volumes of hydrogen. Oxygen condenses upon 
its surface. Platinum, when introduced into a mixture of 
hydrogen and oxygen, causes an explosion. This is due 
to the heat generated by the rapid union of that part of 
the gas absorbed by the metal. The gases are fully ex- 
pelled at red heat. Hydrogen passes through red-hot plat- 
inum. The metal is not permeable to other gases, such as 
oxygen. It is not attacked readily by acids, but is soluble 
in chlorine water and aqua regia. Finely divided platinum 
("platinum black," made by precipitating a solution of 
H2PtClg by zinc) does dissolve in hydrochloric acid on ex- 
posure to the air, due to its decomposition and the liberation 
of free chlorine. When wires of platinum, gold, or silver 
are held under water, and sparked by an electric discharge, 
the metals are converted into a colloidal form, which is solu- 
ble in water. The alkaline hydroxides, sulphides, and 
cyanides attack platinum at red heat. Platinum has the 
same coefficient of expansion as some glass. As it conducts 
electricity it is fused into incandescent bulbS to serve as 
an electrical connection between the current outside and 
the filament within. Platinum forms various readily fusible 
compounds or alloys with phosphorus, arsenic, and many 
of the heavy metals, as lead, hence these should not be 
heated in platinum vessels. But when a metal is wanted to 
withstand mechanical injury or chemical action, as in mak- 
ing standard meters, or fountain pen points, an alloy of 



THE PLATINUM METALS 



I«I 



platinum and iridium is employed. On account of its in- 
fusibility and resistance to the attacks of chemicals, plati- 
num is used extensively in making important apparatus 
for the chemical laboratory and stills for the concentration 
of pure sulphuric acid in its manufacture. Platinum 
sponge serves as the '^ contact " material, that is, catalytic 
agent, in the manufacture of sulphur trioxide. The price 
of platinum is very high and variable. Extension of its 
use and fortuitous circumstances attending its extraction 
from its ores are the causes of this fluctuation. A heavy 
rainy season in the Caucasus and Russian peace increase 
the output with a lowering of the price. 

GROUP VIIL — The Gadolinite Metals 



Element" 


Samarium 


Europium 


Gauoliniu./. 


Derivation of 
name 


von Samarski 


Europe 


Gadolin 


Symbol 


Sa 


Eu 


Gd 


Discoverer 


de Boisbaudran 


de Boisbaudran 
and Demargay 


Marignac 


Date 


1879 


1892 and 1896 


1880 


Atomic weight 


150.4 


152.0 


157.3 


Appearance 


Whitish-grey 
metal 


Not yet isolated 


Metal 


Specific gravity 


7.8 







Melting point 


+ i30o°to + i4oo° 







EXERCISES 

I. Compare the properties of the members of the three series 
of Group VIIL 2. How may we arrive at the formula PdgH ? 



182 



GENERAL INORGANIC CHEMISTRY 

















(U 










1 <u 










-1-^ 






CO 


7. 




0^ 


o 




On 


3 


Lr> 




< 


< 
PL, 












> 


C^ 


+ 


s 
§ 














'in 








<^ 
















p 




^ 
















z 

g 

J 




o 




-t-J 










o 


5 




,1^ 




O 

CO 


ON 






8 


Pi 


^ 










'"' 


M 


+ 


> 




c3- 
















<: 






































Cd 




















S 




1:^ 

o 




^ 






CAl O U 




f' 






o 


CA) 


c3 


o 


ON 


III 


t 


o 
o 


H 


i 


"^■^ 


o 


c 


oo 


§^ 


to 5^ o; 


(^ 


N 




6 


1 




f^ 




03 


CS 


+ 






m 










OJ 








5 


i3 

£1m 


^3 


to 


ro 


l-^ 


IS 


^ 


o 

8 




< 
►J 

< 






^ 


o 


2e 




+ 




Ph 


rt 




^ 






> 






in 




P^ 










m 








/■~\ 










<u 








s 


2 




o 


^ 


On 






o 




5 




S 


iS 
"o 

^ 


O 

OO 


■ o 




M 


+ 


^ 




VQ. 










c75 






g 






































H 




















<: 
pm 
H 
O 


D 
1 

a 


5^ 


5 , 


1/1 




oo 


o 


>> 

biO 




8 

00 

+ 


:3 


rt 










cJ^ 




























OJ 
















H 




S 


















H 










^ 




>-. 






2 


o 








bJO 




'> 


c3 




U 










<u 


rt 






s 


.2 




;_! 




'S 


u 


2 


o 






(U 




^ 


P3 


bjC 


a, 






t^ 


"o 


> 




u 


2 




a 








C/2 


o 
o 

Ol 

Q 


<L) 

Q 


"a 

o 

< 


o 
< 







CHAPTER XXVIII 
HYDROGEN COMPOUNDS OF THE ELEMENTS 

Group VII 

These compounds are known as the halogen acids, and 
have already been considered. 

Group VI 

Hydrogen Monoxide, or Oxygen Dihydride, Water, has 
also been described. 

Hydrogen Dioxide. Hydrogen forms two compounds 
with oxygen, — hydrogen dioxide, or peroxide, H2O2, being 
the second. 

Hydrogen dioxide was first prepared by Thenard in 
18 18. It occurs in small quantities in the atmosphere; 
has been found in rain and snow ; and is formed as a result 
of many chemical reactions. It is produced in very small 
quantities when a jet of burning hydrogen is cooled; but 
is usually prepared by treating certain metallic dioxides, 
as barium dioxide, with sulphuric acid : — 

BaO^ 4- H.2SO4 ^ BaSO^ + H2O2. 

The reaction should be carried out in the cold. 

The hydrated barium dioxide is used. This gives a 
water solution of the substance which is difificult to con- 
centrate. It may be purified partially by freezing and 
pouring off the mother liquor, or by distiUing off the water 
under reduced pressure. 

183 



1 84 GENERAL INORGANIC CHEMISTRY 

It is a colorless, oily liquid, with sp. gr. 1.49; evaporates 
slowly in vacuum, and does not solidify at —30°. It has 
no odor, but attacks the skin when brought in contact with 
it, producing blisters. It is very unstable, decomposing 
into oxygen and water. The decomposition may take 
place with explosive violence. The utmost care should be 
exercised in opening the bottles in which the water solu- 
tion is transported. The oxygen which is liberated is 
in the nascent condition, hence it is a powerful oxidizing 
agent. It bleaches organic coloring matter, liberates iodine 
from potassium iodide, and decomposes ozone : 

H2O.2 + 03^ H^O + 2 O2. 

On account of its oxidizing property, it is used as a dis- 
infectant. It is ordinarily used in dilute aqueous solution, 
*' ten volume," 2.66 per cent, or "fifteen volume," 4 per 
cent solution. It undergoes slow decomposition at ordi- 
nary temperatures, hence the solution may be preserved 
only for a short time. The decomposition goes along 
much more rapidly in alkaline than in acid solutions. 
It has been used for bleaching or " blondining " the hair 
("golden fluid"). 

Silver oxide is reduced to the metaUic state by hydrogen 
dioxide, due to the fact that the liberated oxygen possesses 
a stronger attraction for the oxygen atom in the silver oxide 
molecule than the silver. Hydrogen dioxide is therefore 
a reducing as well as an oxidizing agent : 

Ag^O + H^O^ =^ H2O + O2 + 2 Ag. 

The graphic formula may be written thus : — 

^>0=0, or H— O— O— H. 



HYDROGEN COMPOUNDS OF THE ELEMENTS 185 

TJlc Sulphur Hydrides. There are two of these, — • 
HgS and H2S2. 

Hydrogen SulpJiide, sulphuretted hydrogen, H.2S, is 
found in the gases of certain volcanoes, in sulphur springs, 
in nature as the result of the decomposition of metallic sul- 
phides and organic matter containing sulphur. It is found 
in sewer gas. It may be prepared 

1. By passing hydrogen over heated sulphur: 

H2 + S ^ H2S, or 

2. By the action of acids upon certain sulphides : 

FeS + H2SO4 r±: FeSO^ +t H2S. 

It is a colorless gas, with an odor very disagreeable to 
many people, but with a sweetish taste. It dissolves in 
water ( I : 1.75 volumes), hence it is not collected over water. 
When liquefied, it boils at — 60°, and freezes to an ice-like 
solid at —91°. The hquid has a sp. gr. of 0.9 at —74°. 
It is poisonous, although not violently so. 

It is much less stable than the corresponding oxygen 
compounds, being easily dissociated at + 400°, or slowly 
by the action of the oxygen of the air : 2 H2S +03=^ 
2 H2O + I 2 S ; or at once by the halogens : H2S + Cl2=> 
2 HCl +1 S. Its solution does not preserve its strength 
long on account of oxidation. It is slightly acid in char- 
acter, and is used extensively in analyses to precipitate 
the insoluble metallic sulphides. The gas burns with a 
blue flame. If the amount of oxygen is Hmited, the hydro- 
gen burns and the sulphur separates. 

Hydrogen Disnlphide, H2S2, is prepared in the same way 
that the dioxide is: CaS2 +^2 HCl^CaCl2 + H2S2. It 
is a yellow, mobile liquid ; decomposes into sulphur and 
H2S ; has a very disagreeable odor, some bleaching power, 
and is poisonous. 



1 86 



GENERAL INORGANIC CHEMISTRY 



SeleniiLin Hydride, hydrogen selenide, or selenuretted 
hydrogen, H2Se. Selenium forms but one compound with 
hydrogen, which is a colorless gas with an odor like hydro- 
gen sulphide, but more disagreeable and persistent. It is 
soluble in water, giving an acid solution. 

Tellurhnn Hydride, hydrogen telluride, telluretted hy- 
drogen, H2Te, is made in the same way. It is poisonous. 



Properties 


OF THE H 


YDRIDES OF GrOUP VI 




Compound 


Molecular 
Weight 


Physical 
State 


Specific 
Gravity 


Dissociation 
Temperature 


Reaction 


H,0 

H,S 
H2S2 
HgSe 
H,Te 


18.02 
34.02 

34-07 

81.2 
129.6 


Liquid 
Liquid 

Gas 

Liquid 

Gas 

Gas 


I 

1-5 

1. 1 7 (air) 

2.81 
4.48 


+ 1800° 
+ 100° 
+ 400° 

Ord. temp. 

+ 150" 
Low temp. 


Neutral 
Neutral 
Acid 
Acid 
Acid 
Acid 



Group V 

The typical hydride of nitrogen, namely, ammonia, NH3, 
has been considered. There are two others, however; 
namely, hydrazine and hydrogen trinitride. They are con- 
sidered to illustrate the striking change in properties of the 
compounds of two elements when they are present in differ- 
ent proportions. Ammonia, NH3, combines with another 
hydrogen to form ammonium, NH4, which acts as a radi^ 
cal, forming an ammonium amalgam. 

Hydrazine, diamide, N2H4, was separated in 1895 by 
Lobry de Bruyn. It may be graphically represented in 



this manner : 



>N— N< 



H 



which indicates that it is NH3, 
replaced by NH2 (a radical). 



H' 

in which i H 



has been 



HYDROGEN COMPOUNDS OF THE ELEMENTS iSy 

It is prepared indirectly by boiling triazo-acetic acid with 
sulphuric acid, which gives hydrazine sulphate. This salt is 
decomposed by a strong base, just as ammonium sulphate is. 

It is a liquid with a pecuUar odor, exceedingly soluble 
in water, b. -p. + 113.5°; sp.gr. 1.4; stable at + 300° ; very 
caustic, and attacks glass. It is basic and forms com- 
pounds with the acids, similar to ammonia. It is a power- 
ful reducing agent. 

Hydi'azoic Acid, hydronitric acid, hydrogen trinitride, 
azoimide, HN3, was discovered in 1890 by Curtius. It is 
a colorless, mobile liquid at low temperatures, but ordinarily 
a gas possessing a very pungent, disagreeable, penetrating 
odor, which produces a headache. It is poisonous. The 
acid is unstable, decomposing with violence when the liquid 
is warmed. The hydrogen is replaceable by metals as in 
hydrochloric acid. The salts formed are very explosive. 

PHOSPHORUS HYDRIDES 

There are also three compounds of phosphorus and 
hydrogen. 

Phosphine, phosphuretted hydrogen, PHg, is prepared — 

1. Reaction between calcium phosphide and hydro- 
chloric acid, or water : — 

Ca3P2 4- 6 HCl :± 3 CaCl2 + \2 PH3. 

2. By heating phosphorus in potassium hydroxide dis- 
solved in water : — 

3 KOH -f 4 P + 3 HP z^ 3 KH2PO2 + t PH3. 

During the reaction the air must be excluded. 

It is a colorless gas, with a very disagreeable, garlic-like 
odor ; soluble in water, and in very dilute form has a caus- 
tic taste. It ignites at -f 100°, burning with oxygen to 
form white fumes of P2O5. It is easily decomposed by heat ; 
and is very poisonous and basic like ammonia, forming 



I88 GENERAL INORGANIC CHEMISTRY 

compounds with the acids, as PHg + HI == PH^I, phos- 
phonium iodide. 

Usually in preparing the gas it takes fire spontaneously 
on coming in contact with the air. This is due to the 
presence of P2^4- 

Liqicid Hydrogen Phosphide, V^l^, which is prepared at 
the same time, may be separated by carefully cooling 
the products as they are given off. It is a very unstable 
liquid ; inflammable at ordinary temperatures and decom- 
posed by slight heating, or on exposure to light, into the 
other two hydrides : — 

Solid Hydrogen Phosphide, V^W^. The existence of 
this body is not clearly estabhshed. It seems to be a yel- 
low powder, decomposed at + 70° ; it takes fire at -f 100°. 

ARSENIC HYDRIDES 

Arsine, arsenuretted hydrogen, AsHg, was first observed 
by Scheele in 1775. 

It is prepared by the action of nascent hydrogen upon 
compounds of arsenic : — 

AS2O3 + 6 H2 r±: 3 H2O + f 2 AsHg. 

This method of production is used in what is known as 
Marsh's test for arsenic. 

It is a gas, m.-p. — 113.5°, somewhat soluble in water, 
which solution decomposes on standing in the air. It 
burns with a blue flame, with the formation of clouds of 
AS2O3. When the flame is cooled by inserting a cold 
object, like a piece of porcelain, the hydrogen burns, while 
the arsenic is deposited in the metallic form. The black 
deposit on the porcelain is soluble in sodium hypochlorite, 



HYDROGEN COMPOUNDS OF THE ELEiMENTS 



189 



insoluble in ammonium sulphide, and soluble in nitric acid, 
which solution after evaporation gives a red color with 
silver nitrate. The gas is decomposed if passed through 
a hot tube. It is very poisonous. 

Solid Hydrogen Arsenide, AS2H4, is a reddish brown, 
silky substance which is not well known. 

ANTIMONY HYDRIDE 

Hydrogen Antimonide, stibine, antimonuretted hydro- 
gen, SbHg, is prepared in the same way that arsine is 
and has very similar properties, being a gas with a 
very disagreeable odor and taste, very poisonous, and 
easily decomposed by heat. It burns with a greenish blue 
flame, with the production of white fumes, Sb^Og. A 
black deposit of metallic antimony is produced when a 
cold object is inserted in the burning gas, as in the case 
of arsine. This black deposit is insoluble in sodium hypo- 
chlorite, soluble in ammonium sulphide, and does not 
give the red color when treated with nitric acid and silver 
nitrate. 

PROPERTIES OF THE HYDRIDES OF GROUP V 



Compound 


MoL. Wt. 


Physical 
State 


Sp. Gr. 


B.-P. 


SOLUBI'LITY 

IN Water 


Reaction 


NH, 

N,H, 

N,H 

PH.. 

P,H, 

P,H, 

AsH, 

As,H, 

SbH3 


17.02 

34.02 
66.03 

78.02 

123.2 


Gas 

Liquid 

Gas 

Gas 

Liquid 

Solid 

Gas 

Solid 

Gas 


0.59 

1.003 



1. 18 
1. 01 

2.69 

4-3 


-34° 
+ 113-5 

-3r 
+ .7° 
-40° 
-18° 


1 148 V. : I 
Sol. 
Sol. 
Sol. 

.5 V. : I 
4 V. : I 


Str. base 
Base 
Acid 
Base 

Neutral 
Neutral 



190 GENERAL INORGANIC CHEMISTRY 

GROUP IV 

The carbon type has been discussed. Others are con- 
sidered under the head of Organic Chemistry. 

Two Silicon Hydrides are known, SiH^ and Si2Hg. The 
latter was discovered by Moissan in 1902. 

Silicon HydiHde, SiH^, is prepared by treating a metal- 
lic silicide with an acid : — 

SiMg2 + 4HC1^2MgCl2 + tSiH4. 

It is a colorless gas, heavier than the air, fairly stable, 
but decomposed at red heat When produced with hydro- 
gen, it is spontaneously inflammable. As a rule some 
free magnesium remains in the making of SiMg2, so the 
gas takes fire as it is produced. 

METALLIC HYDRIDES 

There are few metallic hydrides known. They were 
mentioned under the elements which form them. 

EXERCISES 

1. In concentrating H2O2 by the freezing method, would the 
dioxide be in the mother liquor poured off or in the crystals ? Give 
the reasons for your answer. 

2. Write the equation for the production of hydrogen selenide 
from FeSe. 

3. Write the equation for the preparation of hydrogen telluride 
from ZnTe. 

4. Zinc arsenide (ZuaAsg) yields arsine with hydrochloric acid. 
Write the reaction. 



CHAPTER XXIX 

HALOGEN COMPOUNDS OF THE ELEMENTS, OR HALIDES 
— GROUPS I, II, AND III; PHOTO-CHEMISTRY 

The halogens combine with almost all the elements, 
forming fluorides, chlorides, bromides, and iodides. The ele- 
ments of strongly electro-positive character form the more 
stable compounds ; for example, NaCl is stable, while CI2O 
is unstable. The compounds of electro-positive elements 
are salts and soluble in water, with the following excep- 
tions, namely, the chlorides, bromides, and iodides of silver ; 
the cuprous, aurous, mercurous, thallous, lead, and plati- 
nous chlorides, bromides, and iodides ; and the fluorides of 
copper, calcium, strontium, and barium. 

The Jialides may be formed according to one or more of 
four type methods : — 

1. By the direct union of the elements : — Zn -f C\~^ 
ZnCl2. 

2. By the action of the halogen acids on the metals or 
the metallic oxides : — Zn + 2 HCl r±r ZnClg + f H2 ; 

ZnO -f 2 HCl z^ ZnCl^ + H^O. 

3. By the action of the halogen upon the oxide, mixed 
with carbon, at high temperatures : — 3 CI2 + AI2O3 + 3 C 
z±2AlC]3-ft3CO. 

4. By double decomposition and the formation of the 
insoluble halides : — AgNOa + NaCl r± NaN03 + I AgCl. 

Halides of Group I 
Positive Series. Sodium, potassium, and ammonium 
fluorides are soluble, crystalline bodies which are used as 

191 



192 GENERAL INORGANIC CHEMISTRY 

fluxes. Lithium, potassium, sodium, rubidium, and cesium 
chlorides, bromides, and iodides are all easily soluble in 
water. 

Sodium Chlojnde, common salt, NaCl, is the chief alka- 
line chloride and most abundant compound in which sodium 
and chlorine occur. It occurs: i. In sea-zvater, which 
contains 3.5 per cent of solids, consisting of 

Sodium Chloride (NaCl) 76.4970 Potassium Chloride (KCl) 1.98% 

Magnesium Chloride (MgCl2) 10.20% Magnesium Bromide (MgBro) 1 « 0/ 
Magnesium Sulphate (MgSOi) 6.5170 Calcium Carbonate (CaCOs), etc. j ' 
Calcium Sulphate (CaSO^) 3.97 7o 

Sodium chloride is obtained from sea-water or salt lakes 
by making salt gardens ("salt harvesting"), where the heat 
of the sun is utilized for concentration, which causes the 
separation of crystals of the less soluble constituents. 

2. As rock salt, which is found in large deposits in 
Germany, Spain, Austria, and the United States, as the 
remnants of anciently evaporated seas or lakes. Some of 
it is so pure that it may be ground at once for use, but it is 
usually contaminated with iron oxides, clay, and sand, and 
requires purification. That found in New York, Pennsyl- 
vania, Kansas, California, Utah, and Louisiana is purified. 

3. As salt brines derived from springs, lakes, and wells ; 
that is, waters which have come in contact with beds of 
rock salt. The brines are evaporated by exposure in the 
air to the sun's heat by trickling down ricks of twigs. 
Large crystals, known as ''solar salt," are thus obtained. 
Brines, as a rule, however, receive special treatment, and 
are evaporated by fuel heat. 

Small amounts are often caught up along the seashore 
by the wind and carried far inland. It is present in very 
small amounts in almost all soils and inland waters. More 
than a small fraction of a per cent in the soil is injurious to 



HALOGEN COMPOUNDS 193 

It is a constituent of most animal secretions 
and is necessary for animal life. 

Crude salt contains several impurities, one being magne- 
sium chloride, which attracts moisture and gives the salt a 
bitter taste. The "caking" of table salt is due to such 
impurities. Pure sodium chloride is a white substance, 
crystallizing in cubes, forming hats or hoppers, sp. gr. 2.13, 
m.-p. + 815", volatile at a white heat. It is about equally 
soluble in hot and cold water; 100 parts at 0° take up 36 
parts of NaCl; at -f 100°, 39 parts. It is insoluble in alcohol. 
It is used in food, in making glass, glazing of pottery, and 
as the main source of many sodium and chlorine compounds. 

Potassium Chloride is often found along with sodium 
chloride, though not so abundantly. It occurs as sylvite 
(KCl) and in carnallite (KCl, MgCla, 6 HgO). These 
impure forms are used as fertilizers and as a source of 
material for the preparation of potassium compounds. 
The chlorides are not suitable for fertilizing certain plants, 
as beets and tobacco. They produce a bitter taste and a 
slow-burning leaf. 

Potassium Bromide and Iodide are important halogen 
compounds, used extensively in medicine and photography. 
They are usually prepared in an indirect way, as follows : 
bromine and iodine are allowed to act upon iron in the 
presence of water : — 

Fe + l2:±Fel2. 
Potassium carbonate is then added to the ferrous iodide : 

Fel2+ K2C03i±|FeC03+ 2 KI. 
The solution is evaporated and the salts purified by recrys- 
tallization. One hundred parts of KI dissolve in 73.5 parts 
of water. 

AmmonijLin Chloride, sal ammoiiiaetim, NH^Cl, may be 
appropriately mentioned here, as the supposititious NH^ 



194 GENERAL INORGANIC CHExMISTRY 

acts like an alkali metal. It is made largely from the 
ammonia water of gas works. The liquor is made alkaline 
and boiled. The escaping ammonia gas is absorbed in 
hydrochloric acid. It is a white crystalline substance, very 
soluble in water. When heated, ammonium chloride sub- 
limes. 

The molecular weight of a substance easily convertible 
into a gas is determined by measuring the volume occupied 
by a definite weight, when thoroughly gasified ; that is, its 
vapor density. For example, 119 mg. of chloroform oc- 
cupy 22.24 cc. when the values obtained by experiment are 
reduced to 0° and 760 mm. pressure. The molecular 
weight of chloroform (CHCI3) is actually 119.5. In the 
case of ammonium chloride (NH^Cl), we should expect 53.5 
mg. to occupy 22.24 cc. (reduced to zero and normal pres- 
sure). In fact, experimentally we obtain twice that volume. 
26.76 mg. fill 22.24 cc. When heated to -f 280°, ammo- 
nium chloride begins to dissociate, and it is complete at 
+ 380 , into free ammonia and hydrogen chloride: — 

NH4C1:;±NH3+ HCl. 

They recombine at once on cooling. We may now under- 
stand why the half value is obtained. 17 mg. of NHg 
(14 + 3 = 17) would occupy 22.24 cc. ; 36.5 mg. of HCl 
(i + 35-5 = 36.5) would occupy the same volume. If the sal 
ammoniac did not dissociate, 53.5 mg. (14-1-4 + 35.5 = 53-5) 
would do the same. As double the volume is occupied, two 
gases are produced. They may be separated when disso- 
ciated. 

The dissociation of ammonium chloride is of advan- 
tage in its use in soldering. The hot iron liberates free 
hydrogen chloride, which attacks any adhering metallic 
oxide. 



HALOGEN COMPOUNDS 195 

Negative Series. The halides of the negative series, 
cuprous chloride, silver chloride, and aurous chloride, as 
as well as the bromides and iodides, are insoluble in water. 
Copper, also, forms cupric chloride (CUCI2), which is a blue 
salt, very soluble in water. Gold forms an auric chloride 
(AuClg), which is quite soluble and used in photography. 
They form many double salts, one of which is CuClg, 2 KCl, 
which dissolves iron. Silver chloride, bromide, or iodide 
is formed by precipitation. They are curdy solids, from 
white to yellow in color, which darken with loss of the halo- 
gen when exposed to light. Photography depends very 
largely upon this change. 

PJiotograpJiy may be understood, in part, by a special 
case. Dry plates may be made by covering a piece of 
glass or celluloid with an emulsion of gelatine in which 
silver bromide (AgBr) is suspended. When a plate is 
exposed, although no visible alteration in the bromide is 
observable, it becomes apparent when it is developed. The 
silver bromide is reduced to a lower bromide (Ag2Br) by 
the influence of light. The longer the exposure, which 
usually is only a fraction of a second, the more extended 
the reduction. A developer acts in the same way, reduc- 
ing the silver bromide to metallic silver. Inasmuch as 
some of the bromide is already partially reduced by the 
light, the reducing agent, if allowed to remain in contact 
with the emulsion a limited time, completes that reduction 
more quickly than it reduces the unchanged bromide. In 
fact, the reduction of both proceeds at the same time, but 
one more rapidly than the other ; therefore, the plate is 
kept in the developer only a limited time, depending upon 
circumstances. The most commonly used developers are 
alkaline solutions of the sodium salts of hydroquinone 
and pyrogallic acid, but we may illustrate the chemistry 



196 GENERAL INORGANIC CHEMISTRY 

of the process by employing potassium ferrous oxalate 
[K2Fe( 0204)2]. To simplify matters we make use of the 
ferrous, which is oxidized to ferric, oxalate in the equation, 
and a mixture of argentous and argentic bromide : — 

3 FeC204+2 AgBr + Ag2Br ^ Fe2(C204)3+FeBr3 + 4 Ag. 

The unreduced silver bromide (AgBr) is then dissolved 
by a solution of sodium thiosulphate (commonly called 
''hyposulphite of soda," or *'hypo"), which does not af- 
fect the metallic silver, but serves as 2i fixer. The ^'neg- 
ative,'' on which the parts which were brightest are now 
opaque, and the darkest transparent, is thus produced. 
When the picture is printed from the negative, the light 
and dark, with their shades, are again reversed. The 
printing paper is coated with a silver halide emulsion which 
undergoes a similar treatment. In toning, a portion of the 
silver is dissolved, being displaced by gold or platinum, 
which is deposited in its place : — 

NaAuCl4 + 3 Ag ^- NaCl + 3 AgCl + Au. 
The thin film of the different metal gives a characteristic 
color or effect to the print. 

Halides of Group II 

Positive Series. The fluorides of the positive series are 
insoluble in water. Calcimn fluoride, fluorspar, or fluorite, 
CaF2, is the most important, and occurs widely distributed 
and is fairly abundant. Frequently it occurs in beautiful 
crystals, variously colored by the impurities present. It 
is used extensively in metallurgy as a flux, hence its name, 
and as a source of hydrofluoric acid. Many fluorspars pos- 
sess the property of fluorescing and phosphorescing under 
the influence of different exciting agencies, as heat. X-rays, 
and Becquerel rays. 



HALOGEN COMPOUNDS 197 

The other halogen compounds are soluble in water. 
Magnesium, calcium, and zinc chlorides are deliquescent. 

Magnesium CJdoride, MgClg, occurs in sea-water and 
causes the salt obtained by its evaporation to attract mois- 
ture and have a bitter taste. It is one of the constituents 
which give permanent hardness to waters. It is decom- 
posed by steam, also by heat, free HCl being given off 
and the oxide, or an oxychloride, being formed. The 
anhydrous chloride may be obtained by evaporating the 
solution with an excess of ammonium chloride. 

Calcium Chloride, CaCl2, in different forms, granulated 
and fused, is used as a desiccating agent. 

Negative Series. Zinc Chloride, ZnCl2, is used as a dehy- 
drating agent in organic chemistry, and is so powerful that 
it is caustic in its action upon cellulose. In the diluted 
form it is used as a disinfectant and in embalming fluids. 

Mercury forms two chlorides: 'tnerciiric cJiloride, ** bichlo- 
ride," corrosive sublimate, HgC]2, and mercnrons chloride, 
calomel, Hg2Cl2. Both sublime easily. The mercuric salt 
fuses before subhmation. The mercurous salt is insoluble 
in water. It is used as a purgative in medicine. It ap- 
pears to be decomposed by acids and it is regarded as 
dangerous to have acid or highly saline food accompany 
or immediately follow it, when taken as medicine, on ac- 
count of the production of mercuric chloride, which is a 
poison. Mercuric chloride is fairly soluble in water, more 
soluble in an ammonium chloride solution. It is soluble 
in alcohol and ether, which is unusual for metallic salts. 
It is a powerful germicide and is used in medicine as an 
antiseptic, in solution i : 1000 or i : 2000. 

Mercury also forms two iodine compounds : mercuric 
iodide, Hgl2 (red), and mercurous iodide, Hgl (yellow). 
The former is insoluble in water, but readily soluble in a 



198 GENERAL INORGANIC CHEMISTRY 

solution of potassium iodide, forming a double iodide, 
(Hgig, 2KI), which is a more efficient germicide than 
mercuric chloride. 

Halides of Group III 

Boron Fluoride, BFg, illustrates the type. Boron chlo- 
ride, BCI3, is a colorless liquid, readily decomposed in water 
with the formation of hydrogen chloride and boric acid : — 

BCI3+ 3H20z^f 3HCI+ |B(0H)3. 

Alumimim CJiloidde, AICI3, is a white crystalline solid 
which is very deliquescent. It forms double chlorides 
with the alkahne chlorides, and is used in the preparation 
of aluminum. It is used in preparing many carbon com- 
pounds. On evaporating a solution of aluminum chloride 
in water, it is decomposed : — 

AlClg+s HOH r±3 HC1+|A1(0H)3. 

The other members of this group also form the type, 
MCI3, M standing for any member of the group. They 
do not decompose as readily with water. Thallium also 
forms another chloride, TlCl, which is insoluble in water. 

EXERCISES 

1. Why do we use the volume 22.24 cc. for milligrams in 
weight in determining the molecular weight of a substance by 
its vapor density? 

2. One hundred parts of water dissolve 2iZ parts of ammonium 
chloride at 0°, and 73 parts at 100°. Suppose we had a satu- 
rated water solution of a mixture of sodium and ammonium 
chlorides and cooled it to zero, which would separate out, or if 
both, in what proportion? 



CHAPTER XXX 

HALOGEN COMPOUNDS OF THE ELEMENTS, OR HALIDES. 
— GROUPS IV, V, VI, VII, AND VIII 

Group IV 
Positive Series 

Cai'bon Tetrachloride. Carbon does not readily combine 
with the halogens, but several compounds have been made 
by the action of chlorine upon the hydrocarbons : — • 

CH4+ 4 Cl2=^4 HCl + CCI4 (tetrachlormethane). 

This is also prepared by the treatment of carbon disul- 
phide with chlorine. It is distinguished from the hydrogen 
compounds by not burning readily. It is a liquid, sp. gr. 
1.63, which boils at -\- J%° . It is an excellent solvent for 
many organic substances. 

The halogen compounds are insoluble liquids in the case 
of chlorides, and solids in the case of bromides and iodides. 
At + 200° carbon tetrachloride is decomposed by water : — • 

CCI4 + 2 H20=±4 HCl + CO^. 

Silicon TetracJiloride is formed by the action of chlorine 

upon amorphous silicon, or a heated mixture of silica and 

carbon, or magnesium silicide (Mg2Si). It is a strongly 

fuming liquid that is decomposed at once by water : — 

SiCl^ + 4 H20^4 HCl + I Si(OH)4. 

Silicon Tctrafluoride, SiF4, is formed by the action of 
hydrofluoric acid upon silica : — 

4 HF + 5102^^ 2 H2O 4- 1 SiF^. 



200 GENERAL INORGANIC CHEMISTRY 

It is a heavy, colorless gas, sp. gr. 3.07. This in turn 
reacts with water : — 

SiF4 + 4H20^4HF + |Si(OH)4, 
or 3 SiF^ + 4 H20z±riSi(OH)4 + 2 H2SiFg 

(hydrofluorsiHcic acid, or hydrogen siUco-fluoride). The 
latter is an unstable acid, forming a series of stable salts 
known as fluor-silicates. Silicon tetrafluoride is a by- 
product in the manufacture of phosphatic fertilizers when 
fluorides are present in the phosphate rock used. 

Titaniitm TetracJdoride is a liquid which is decomposed 
by water to the oxychloride : — TiCl4 + Yi^O-^\ 2 HCl + 
TiOCl2. Titanium tetrachloride, by reduction, forms a 
tricJiloride, TiClg, a powerful reducing agent, which readily 
absorbs oxygen. It is used in making coal tar colors. 

Zirconhim and TJioriuni form tetra- and oxyhalides 
which are white crystalline bodies. 

Negative Series 

Tin dissolves in hydrochloric acid to form stannous 
chloride : — Sn + 2 HCl:r^SnC]2 -f \ H2. By the action of 
chlorine on metallic tin, stannic cJdoride^ or tin tetrachlo- 
ride, SnCl4, is formed. Stannous chloride is a solid; soluble 
in water, but quickly decomposed into insoluble stannous 
oxychloride and hydrochloric acid. It is a strong reducing 
agent. Stannic chloride is a fuming liquid which com- 
bines with three parts of water with "hissing," producing a 
white crystalline solid, soluble in water. It is decomposed 
either by heat or on allowing it to stand at ordinary tem- 
perature : — SnCl4 + 4 H20r± t4 HCl + H2O H-SnO(OH)2 
(metastannic acid). 

Lead Chloride, PbCl2, is formed by the action of a sol- 
uble chloride upon any soluble salt of lead: 

Pb(N03)2 + 2 NaCl !>: 2 NaN03 + I PbClg. 



HALOGEN COMPOUNDS 201 

It is only slightly soluble in cold water. It dissolves in 
hot water and crystallizes on cooling. 

Lead Tetrachloride, PbCl4, is said to be formed when 
lead dioxide (Pb02) is dissolved in very cold hydrochloric 
acid. It is unstable, being decomposed by heat or solu- 
tion in water to PbCl2 + CI2 ; consequently, lead dioxide 
when treated with hydrogen chloride yields free chlorine : — 

Pb02 + 4 HCl T± \ PbCl2 + 2 H2O + \ CI2. 

Lead Lodide, Vhl^, is formed in the same way that PbCl2 
is, but is less soluble. It is a brilliant yellow substance 
which crystallizes from hot water in golden scales. 

LLalidcs of Group V 

The halogen compounds of nitrogen are among the most 
unstable compounds known. When chlorine acts upon an 
excess of ammonia, nitrogen is liberated. If, however, an 
excess of chlorine is allowed to act upon ammonia, nitrogen 
trichloride, NCI3, is formed. It is an oily liquid which 
explodes with great violence on slight elevation of tempera- 
ture or the least shock. 

Nitrogen Lodide [NI3 (.^), more likely N2H3I3, or NI3, 
NH3]. When iodine is allowed to act upon strong am- 
monium hydroxide, a grayish black compound, containing 
nitrogen, hydrogen, and iodine, called nitrogen iodide, is 
formed. This dark body may be filtered off and allowed 
to dry spontaneously. When dry, the slightest touch will 
suffice to explode it ; when moist, it gradually decomposes. 

Phosphorus, Arseriic, Antimony, and Bismuth unite with 
chlorine to form trichlorides : PCI3, ASCI3, SbClg, BiClg. 
Phosphorus and arsenic trichlorides are Hquids ; the others 
are solids. Antimony and bismuth trichlorides, on account 
of their soft consistency and easy fusibility, were known 



202 GENERAL INORGANIC CHEMISTRY 

to the alchemists as ''butter of antimony" and "butter of 
bismuth." On adding an excess of chlorine, PCI5, AsClg 
(unstable above — 30° C), and SbCl^ are formed. Phospho- 
rus pentachloride is a white solid. Antimony pentachlo- 
ride is a liquid. 

These are all decomposod by water, according to the 
following reactions : — 

PCI3+ H20r>POCl(phosphorous oxychloride)+ 2 HCl, 
ASCI3 + HgOz^iAsOCl (arsenious oxychloride) -h 2 HCl, 
BiCl3+ H^b^^iBiOCl (bismuth oxychloride)-}- 2 HCL 

Phosphorus trichloride and pentachloride, as well as oxy- 
chloride, with excess of water are completely decomposed : — 

PCI3 + 3 H2O =±3 HCl + P(0H)3 (phosphorous acid), 
PCI5 + H26^2 HCH- POCI3 (phosphoric oxychloride), 
POCI3 + 3 H20^> 3 HCl + PO (0H)3 (orthophosphoric 

acid), 
PCI5 + 4 H20z^5 HCl + P0(0H)3. 

The oxychlorides of antimony and bismuth are insoluble 
in water. They are held in solution in water by the pres- 
ence of much free hydrochloric acid. Tartaric acid and 
sodium chloride also prevent antimony oxychloride from 
precipitating when water is added. 

Halides of Group VI 

The oxygen halides will be considered under the head 
of the oxides. 

SiilpJmr Chlorides. When chlorine is led into melted 
sulphur, S2CI2, a heavy, yellowish red liquid is formed. 
It is a solvent for sulphur, and the solution is used in vul- 
canizing rubber. When chlorine is led into S2CI2 at a 
moderately low temperature, + 6° to 4- 8°, SCI2 is formed; 



HALOGEN COMPOUNDS 203 

when chlorine is led into this at — 20°, SCI4 is formed. 
These two, also, are liquids. 

With the members of the positive series of this group 
chlorine unites directly, and several compounds are formed 
with each element which do not require further considera- 
tion. They are as follows : — 
CrClo 



WCl, 



Halides of Group VII 

The halogens form several unstable compounds by direct 
union with each other; namely, ClBr, ClI, and ICI3. 

With manganese the halogens form compounds accord- 
ing to the type MnX2. It is barely possible that MnCl^ 
may exist, at low temperatures. The manganese hahdes 
resemble the negative series of Group II. 



CrCl, 








MoCl, 


IMoCl^ 


M0CI5 






WCl, 


WCl, 


WClg 


UCI3 


UCl, 


UC1,5 





Halides of Group VIII 



FeCl^ FeClg C0CI2 



RuCl^ RuClg 

SmClg 

OsClo OsClg OsCl, 



RhCl^ 

EuCl. 



NiCl, 

PdcC rdo, 

^ GdCl, 



IrClo IrCl, PtClo PtCl, 



All are made by General Methods I and II. 

Nickel and cobalt act only as bivalent elements with the 
halogens, giving NiCl2 (green) and CoCU (rose). Nickel 
CJdoride, NiCl2, usually crystallizes with 6 H2O ; it loses 
its water on heating and becomes yellow. Cobalt 
Chloride, CoC]2, combines with 6 H2O, giving monoclinic 
crystals. When it becomes anhydrous it is blue in color. 
Characters made with this solution on paper are almost 



204 GENERAL INORGANIC CHEMISTRY 

invisible, but become distinct when warmed. The solution 
is therefore used for one kind of " sympathetic ink." 

Ferrous Chloride crystallizes from aqueous solution in 
green, monoclinic crystals which become brown, due to 
deliquescing and oxidizing in the air. The anhydrous prep- 
aration is made by passing HCl over heated iron. It is a 
white mass which may be sublimed at a red heat. It ab- 
sorbs chlorine and is at once converted Vi\X.o ferric chloride 
(FeClg or FcgClg), a yellow, crystalline mass, very soluble 
in water, alcohol, and ether, b.-p. -f 200°. Vapor density 
determinations at + 320 to + 420° indicate that the for- 
mula Fe2Clg is correct; at + 750 to + 1050°, FeCl3. 

Palladium Chloride is a brown, deliquescent mass which 
forms a double salt, K2PdCl4. Palladium Iodide, Pdig, is 
a black mass, insoluble in water, while the chlorides and 
bromides are soluble in water. Palladic Chloride, PdCl^, 
or hydrochlor-palladic acid, H2PdClQ, is formed when the 
metal is dissolved in aqua regia. 

Platinous Chlofide, PtCl2, is a green powder, insoluble 
in water. It is obtained by heating platinum tetrachlo- 
ride, PtCl^ to 4- 200°. It forms double salts, as KgPtCl^. 
Platinic Chloride, PtCl^, or hydrochlor-platinic acid, 
H2PtC]g, is obtained in a similar manner. It crystal- 
lizes with six molecules of water in brown-red prisms. 
The chlor-platinates give a series of double crystalline 
salts, of which PtCl^, 2 KCl is an example. 

Ruthenium Trichloride, RuClg, when oxidized by nitric 
acid, forms RuClgNO,, and not RuCl^. 

EXERCISES - 

1. Tabulate the chlorides, and their properties, of Group IV. 

2. Write the reactions resulting from adding water to phos- 
phorous tri-iodide ; tri-bromide ; antimony pentachloride. 

3. How may ferric chloride be converted into ferrous chloride? 



CHAPTER XXXI 
DETERMINATION OF MOLECULAR WEIGHTS 

In learning the composition of water, the first compound 
studied in this book (Chap. V), we found that the third 
desirable thing to know of a compound is the molecular 
weight of the body. The determination of the molecular 
weight is closely associated with the atomic weight, and is 
often necessary in settling upon the correct figure to be 
used for the latter. We know of no one method by which 
molecular weights of all classes of substances may be de- 
termined. Furthermore, we know no method applicable to 
classes of substances which has not exceptions. By a com- 
bination of methods, however, a great amount of substan- 
tial information has been accumulated. Extended study is 
necessary to acquire familiarity with the various methods 
that are used. A few typical methods will be discussed 
here and they are presented free from details. 

I. If the substance is readily convertible into a gas, we 
found that the molecular weight might be obtained with 
ease (Chaps. VIII and IX). Many substances are not 
easily converted into gases, and we require other methods 
for determining the molecular weights than that depending 
upon measuring the volume occupied by a known weight 
of gasified substance. Furthermore, there are some sub- 
stances which, on being converted into a gas, occupy a 
larger volume than most substances. Ammonium chloride 
(NH4CI) is an example. When it is converted into a gas, 
it is no longer NH^Cl, but has been dissociated into two 
gases, NH3 and HCl (Chap. XXIX). Each requires its 

205 



206 GENERAL INORGANIC CHEMISTRY 

definite volume for the particular temperature and pressure. 
This apparently exceptional case illustrates a most impor- 
tant phenomenon, and offers a key to the explanation of 
anomalous cases arising with certain other methods which 
are used in determining the molecular weights. 

2. The fact that substances dissolve in a liquid is one of 
the most familiar phenomena of nature — one of the most 
difficult for which to secure a satisfactory and comprehen- 
sive explanation. The term " solution " is usually applied 
to liquids which have dissolved a gas, a solid, or another 
liquid, but this is a limited application. We have learned 
that gases mingle with each other with perfect freedom 
when there is no chemical union. One gas dissolves an- 
other, as it were. One liquid dissolves another, as alcohol 
and water. One solid dissolves another, as shown by 
Roberts-Austen, who placed disks of pure gold in contact 
with pure lead ; after four years he found that the gold 
had penetrated the lead. A solid may dissolve a gas, as 
noted in the absorption of hydrogen by palladium hydride. 
A gas may dissolve a liquid, as we know from the phe- 
nomenon of evaporation. A gas may dissolve a solid, as 
we know from the phenomenon of sublimation. These 
facts have been explained on the ground that molecules 
possess kinetic energy. 

The diffusion of particles of one gas into another, assum- 
ing no chemical action, is fairly rapid. If a wall of un- 
glazed porcelain separates the gases, the diffusion is quite 
rapid. If alcohol, which mixes with water in all propor- 
tions when stirred, is carefully superposed upon water, the 
mixing proceeds, but quite slowly. This may be shown 
by dropping a piece of paraffine into the upper layer of 
alcohol. Paraffine is heavier than alcohol and lighter than 
water. It therefore sinks through the alcohol until it 



DETERMINATION OF MOLECULAR WEIGHTS 207 

reaches that mixture of alcohol and water which has the 
same specific gravity as the paraffine. When the liquids 
are not disturbed, the paraffine remains in nearly the same 
position for months. 

If, however, we separate the alcohol and water by a par- 
tition made of parchment (Abbe Nollet, eighteenth century), 
we observe a comparatively rapid diffusion of the liquids. 
This phenomenon is known as osmosis. Nollet poured 
ordinary alcohol into a glass tube, the lower end of which 
was covered with animal parchment, that is, a bladder, and 
placed the tube in a vessel of water, inserting it until the 
two liquids stood at the same level. The liquid within the 
tube rose apparently contrary to the law of gravity. Pres- 
sure, osmotic p7'essure, was produced. 

Bladders were found to be distensible and not sufficiently 
rigid for quantitative measurement. Traube, finding that 
certain precipitates possess the property of allowing a 
liquid to pass through them, devised an artificial mem- 
brane. It was learned that these membranes, when suita- 
bly deposited, allow the solvent to pass through but hold 
the solute back. They were designated semi-permeable. 
Pfeffer, a botanist, perfected these as follows : a fine- 
grained unglazed porcelain cup was filled with a solution 
of potassium ferrocyanide and then immersed in a solution 
of copper sulphate. When these two hquids are brought 
together a chocolate-colored precipitate of copper ferro- 
cyanide is produced according to the equation, 



2 CuSO^ + K4Fe(CN)g=^| Cu2Fe(CN)6 + 2 K2SO 



Each solution will pass through the pores of the cell, carry- 
ing the solute with it. When they come together the 
precipitate is produced right in the walls and may be 
seen as a fine line when the cell is broken. The pre- 



208 GENERAL INORGANIC CHEMISTRY 

cipitated copper ferrocyanide then acts as a semi-permeable 
membrane. 

Pfeffer found that when a solution of glucose (CgHj20g) 
was placed in such a cell as described and submerged in 
water, the water rose within the cell. Morse has been able 
to cause the solution within to rise as high as 66 feet above 
the surface of the water without. 

The osmotic pressures of many substances have been 
determined. It has been learned that if the molecular 
weight of a substance (in grams) is dissolved in one liter 
of water, it exerts an osmotic pressure equal to 22.24 atmos- 
pheres; for example, 342 g. of cane sugar (C12H22O11 = 
342) or 60 g. of urea (CON2H^ = 60) dissolved in one liter 
of water at 0° exert that pressure. Or, if the molecular 
weight of the substance is dissolved in 22.24 1- of water, 
the osmotic pressure is equal to one atmosphere. Only 
round figures are used here. 

Molecular weights (in grams) of gases occupy the same 
volume under similar conditions of temperature and pres- 
sure (Chap. VIII). That is to say, 2 g. of hydrogen (H2), 
17 g. of ammonia (NHg), and 44 g. of carbon dioxide 
(CO2), each occupy the same volume. If the pressure ex- 
erted by the gas particles upon the restraining walls of the 
vessel is equal to one atmosphere, that is, if the gases are 
measured under 760 mm. pressure, it is found that these 
molecular weights of gases occupy 22.24 ^ at 0°. If the 
pressure is increased sufficiently to cause each gas to oc- 
cupy just one liter, it is found that a pressure equal to 
22.24 atmospheres at 0° is necessary (Law of Boyle and 
Mariotte). This pressure we have learned varies with the 
temperature (Law of Gay-Lussac and Charles). 

Van't Hoff determined that equal volumes of molar 
solutions exert the same osmotic pressure at the same tern- 



DETERMINATION OF MOLECULAR WEIGHTS 209 

perature, and that the pressure varies with the temperature 
in the same way 'that it does with gases. Equal volumes 
of gases under similar conditions of temperature and pres- 
sure have an equal number of molecules (Avogadro). 
Therefore, the pressure which a gas exerts at a given tem- 
perature, if a definite number of molecules is contained in 
a definite volume, is equal to the osmotic pressure which 
is produced by this same number of molecules of most sub- 
stances under the same conditions, if they are dissolved 
in any given liquid (Arrhenius' statement of the Law of 
van't Hoff). 

To determine the molecular weight of a substance, 
therefore, we may take 22.24 1. of water, if that is its sol- 
vent, and add the substance to it until we find that it ex- 
erts an osmotic pressure equal to one atmosphere. The 
number of grams of the solute added is equal to the mo- 
lecular weight. It has' been learned, however, that cer- 
tain substances, as hydrochloric acid, sodium hydroxide, 
and sodium chloride, types of acids, bases, and salts, do 
not obey the law, but exert a pressure of nearly two atmos- 
pheres. Hence, the word ''most'' in the statement of the 
law. The pressure exerted by these three classes of sub- 
stances is of the same order, however. 

3. If we dissolve a solid in water, the boihng point of the 
water is raised and the freezing point is lowered. If we 
dissolve 342 g. of sugar or 60 g. of urea in 1000 cc. of water, 
the boiling point of each solution is 100.52° instead of 
100°; and the freezing point is not zero, but — 1.86° C. 
Equimolecular weights of non-volatile substances in solu- 
tion produce the same elevation of the boiling point of the 
solution or the same lowering of the freezing point (Law 
of Raoult). 

Therefore, if we desire to determine the molecular 



210 GENERAL INORGANIC CHEMISTRY 

weight of a solid, we add enough to one Hter of water to 
cause the boiUng point to rise 0.52° or the freezing point 
to be lowered 1.86°. The amount added in grams corre- 
sponds to the molecular weight. However, van't Hoff and 
others learned by experiment that certain substances, acids, 
bases, and salts, when dissolved in water, do not give the 
same constant elevation of the boiling or lowering of the 
freezing point as generally observed, but figures approxi- 
mately twice, thrice, or multiplicatively as great. These 
exceptional classes of substances give concordant figures 
among themselves. That is to say, HCl, HBr, NaOH, 
KOH, NaCl, and KI give double values ; H2S, Ca(0H)2, 
BaClg give triple values ; and so on. We shall endeavor 
to learn in the next chapter in what way they differ from 
other substances in solution. 

EXERCISES 

1. In determining the atomic weight of oxygen, how was the 
determination of the molecular weight of water important? 

2. How many grams of sodium chloride dissolved in a liter of 
water would be required to elevate the boiling point of the solu- 
tion 0.52°? 

3. How many grams of KI dissolved in a liter of water are 
necessary to lower the freezing point of the solution 1.86° ? 



CHAPTER XXXII 
THEORY OF ELECTROLYTIC DISSOCIATION 

Substances which conduct an electric current, as copper, 
platinum, graphite, and charcoal, are called conductors. 
Glass, porcelain, rubber, and solid sodium chloride, which 
do not conduct the current under ordinary conditions, belong 
to a class called non-conductofs. If the terminals of an 
electric current are placed in pure water or alcohol, there 
is no appreciable flow of electricity. They are also non- 
conductors. In fact, with a few exceptions, all solid non- 
metallic substances, as well as all pure liquids and gases, 
are non-conductors of electricity at ordinary temperatures 
and pressures. If sugar or urea is dissolved in pure water, 
the current does not flow through the solution. However, 
if a little acid, or alkahne hydroxide, or a soluble salt, is 
added to water, the current passes. Such solutions are 
conductors. The passage of the current, however, is accom- 
panied by a decomposition of the solute. They constitute, 
therefore, a special kind of conductors, namely, electrolytic 
conductors^ and are called electrolytes. The process was 
termed electrolysis by Faraday, who learned two very im- 
portant facts in regard to the phenomenon ; namely : — 

First, the amount of a substance decomposed by an electric 
current is proportional to the amount of electricity which 
passes through ; and 

Second, if tJie sa^ne cujTent passes through several electro- 
lytes, tJie amounts of the differejit substances separated fro7ti 



212 GENERAL INORGANIC CHEMISTRY 

the compounds are proportional to the chemical equivalents 
of the substances separated. 

The latter principle may become clearer by illustration. 
If we have a series of electrolytes, as HCl, NaCl, CuCl, 
CuC]2, SnClg, and SnCl^, so arranged that the same cur- 
rent passes through each, we obtain for each gram of H, 
3545 g. CI, 6^.6 g. Cu^ 31.8 g. Cu", 59.5 g. Sn", and 
29.75 g. Sn^^. The equivalence is based on hydrogen, or 
chlorine, which has the same valence. 

If we suspend two pieces of platinum connected to the 
terminals of a direct current in a solution of copper sul- 
phate, we observe the deposition of copper upon the nega- 
tive pole and that the blue color of the solution disappears. 
The copper has traveled from all portions of the solution 
and has accumulated at one place. Faraday called these 
moving particles io7ts (wanderers) ; those going toward the 
anode (positive pole) were termed anions ; those moving 
toward the cathode (negative pole), cations. 




Cations { K OH Anions 



The facts referred to in the last chapter, — namely, that 
molar solutions of three classes of substances (acids, bases, 
and salts) show abnormal elevation of the boiHng point 
or lowering of the freezing point, and exert an abnormal 
osmotic pressure, and as that pressure is analogous to 
gaseous pressure, and that gasified bodies which show 
abnormal pressures (ammonium chloride) are dissociated 
into two or more gases, — caused van't Hoff to suggest that 
these particular substances in solution are decomposed 
into simpler entities, each of which has its influence. In 
short, sodium chloride (NaCl) exists in solution as sodium 



THEORY OF ELECTROLYTIC DISSOCIATION 213 

(Na) and chlorine (CI)- But we have learned that both of 
these elements in the free condition in the presence of 
water decompose it, hydrogen being evolved when sodium 
comes in contact with water and oxygen when water is 
treated with chlorine. Yet we know that neither of these 
gases is given off when common salt (NaCl) is dissolved 
in water. Arrhenius (1887) offered an explanation of the 
statements made above in the Theory of Electrolytic Dis- 
sociation which now has wide acceptance. This theory 
assumes that when sodium chloride is dissolved in water, 
it is dissociated into sodium and chlorine, which do not 
exhibit their normal properties of decomposing water, be- 
cause each carries a charge of electricity which prevents 
it. An ion is therefore an atom loaded with a charge of 
electricity. As compound radicals resemble the atoms, 
the same is true for them ; that is, a solution of ammonium 
nitrate (NH^NOg) in water may be regarded as free NH^ 
and NO3 bearing charges of electricity. 

When the current is started through a solution of an 
electrolyte, the charge is removed from the atom, which at 
once exhibits the properties we are accustomed to associate 
with it. If we pass a current through a dilute solution 
of HCl, NaOH, or NaCl in water, we obtain H at the 
cathode and O at the anode in all three instances. In the 
case of HCL chlorine is liberated, which decomposes water, 
freeing O and reforming HCl, which is again decomposed 
and reformed. In the case of NaOH, sodium is hberated, 
which at once attacks the water, freeing hydrogen and re- 
forming NaOH. Hydrogen dioxide is probably formed, 
and then decomposed into water and oxygen at the anode. 
In the case of NaCl, the Na, when freed from its charge, 
liberates H and forms NaOH, while the CI liberates O and 
forms HCl. By separating the terminals with a porous 



214 GENERAL INORGANIC CHEMISTRY 

partition, we may show that the liquid around the anode 
becomes acid, and that around the cathode basic. If 
there is no partition, HCl and NaOH combine to form 
HgO and NaCl, the latter again dissociating, and so on 
over again. 

The movement of the ions, which is thus demonstrable, 
is sluggish, but the charge borne by each ion is very large. 
The electric current sufficient to deposit 31.8 g. of copper 
(Cu^) will keep a 50-candle-power incandescent lamp glow- 
ing for 13.5 hours. If condensed upon metallic spheres 
held a meter apart, the charge would exert an attraction 
equal to a force of 10^^ tons. 

The cause of this phenomenon of " ionization " is not 
fully understood, but doubtless certain solvents possess 
some specific power which separates the molecules into 
ions. The power of solutions of electrolytes to conduct 
the current increases with dilution. Water is the best dis- 
sociant. When the solution of HCl in water is concentrated 
and electrolyzed, we obtain H and CI, but no O. Pure 
liquid HCl does not conduct the current. On adding a 
trace of water, however, the current flows. Evidently the 
HCl is then the solvent and H2O the electrolyte. 

The theory has been most useful in explaining many 
chemical reactions. For instance, a solution of sodium 
hydroxide may be looked upon as Na+ and OH"* distrib- 
uted in a water medium ; hydrogen chloride as H+ and 
Cl~ ; sodium chloride as Na+ and CI". The anion (0H)~ 
turns a litmus solution blue ; the cation H+ turns it red. In 
NaCl formed from Na+OH" and H+Cl", the anion [(OH)-] 

* An ion is indicated by the small plus or minus sign at the upper right- 
hand corner, the former meaning a cation and the latter an anion. Univalent 
atoms, those carrying one unit charge, have the single sign ; divalent atoms 
have double signs ; and so forth. 



THEORY OF ELECTROLYTIC DISSOCIATION 21 5 

and cation (H+) have combined and no longer exist, while 
the Na and CI neutralize each other, so that a solution of 
salt does not affect the color of a litmus solution. 

Another illustration may be given. Sodium chloride in 
a water solution is dissociated, as noted above. A solu- 
tion of silver nitrate (AgNOg) is an electrolyte, being dis- 
sociated into Ag+ and NOg". If these solutions are mixed, 
Ag+ and Cl~ combine to form an insoluble compound, 
AgCl, which separates from the medium as a precipitate. 
Na+ and NOg" are left in the solution. Attention is to be 
directed here to the fact that chloroform (CClgH), a liquid 
which contains CI in abundance, does not conduct the 
current ; hence it is not an electrolyte. If this is mixed with 
a silver nitrate solution, no precipitate is formed. This 
indicates that chemical reactions at ordinary temperatures 
are facilitated by ionization. 

We may take finally an illustration which involves a gas. 
Aqueous solutions of sulphuric acid (H2SO4) and sodium car- 
bonate (Na^COg) are indicated, when ionized, respectively 
as follows : 2 H++ SO^" and 2 Na++ COg— . When the 
solutions neutralize each other, we have 2 Na+-f SO4 in 
solution. Carbonic acid (H2C0g) is not a stable body, but 
decomposes into H2O and CO2. The latter is a gas and 
escapes from the solvent medium. 

EXERCISES 

1. Write formulas showing what is believed to take place when 
a direct current is passed through weak HCl, NaOH, and NaCl 
solutions. 

2. Suppose the same current passes through solutions of the 
compounds enumerated below, how many grams of each metal 
should separate theoretically for each gram of hydrogen : — 
HCl, NiCl^, FeCl2, FeoClc, AuCl, AuCl., PtCL, PtCl, 



CHAPTER XXXIII 
OXIDES, SULPHIDES, HYDROXIDES, HYDROSULPHIDES 

Oxides 

Members of the positive series of the sixth group do not 
form binary compounds with the positive elements, but do 
with the negative elements. Oxygen forms compounds, 
oxides, with all the elements, except the ** noble gases" 
and fluorine. The oxides of brornine have not been 
obtained in the pure state. With many of the elements 
oxygen forms more than one oxide. The oxides of the 
positive elements are insoluble in water, except those of 
the alkalies and alkaline earths, and these undergo changes 
before solution (hydroxides). The oxides of the negative 
elements generally combine with water. 

Closely related to the oxides is a class of compounds 
containing hydrogen and oxygen, called hydroxides, as 
NaOH, Ca(0H)2, Fe(OH)3,^Zr(OH)4, and so forth. 

General methods for the formation of tJie oxides. 

1. By heating the element or compound in the air or 
oxygen : — 

Cu + Or±CuO, 4P+5 02r±2P205; 

and 2 ZnS + 3 O^ = 2 ZnO + t2 SO^, 

and AS2S3 +90 = As^Og-ff 3 SO2. 

2. By heating hydroxides or certain salts: — 

Cu(OH)2 = CuO + H2O; CaC03= CaO + fCO^; 
2 B(0H)3 - B2O3 + 3 H2O. 

216 



OXIDES, SULPHIDES, HYDROXIDES 21/ 

Hydroxides 
TJie Jiydroxides may be formed, — 

1. By adding water to the oxide : — 

CaO + H2O -±_ Ca(0H)2 ; P^Og -h 3 H2O = 2 P(0H)3. 

2. By the decomposition of water by means of a very 
positive element : — 

2 Na + 2 H2O = t H 2 + 2 NaOH. 

3. By double decomposition, whereby an insoluble hy- 
droxide is formed : — 

FeClg + 3 NaOH = 3 NaCl + |Fe(0H)3. 

The oxides of the more negative elements combine with 
water to form acids ; the oxides of the more positive ele- 
ments unite with water to form bases. The acids and 
bases react to form salts, neutralizing each other with the 
elimination of water. 

(Acid-forming oxide) S03H-H20 = H2S04 (sulphuric acid), 
(Base-forming oxide) Na20 + H2O = 2 NaOH (sodium 

hydroxide), 
(Neutral oxide) 4 Fe + 3 02=2 Fe203 (iron sesquioxide), 
(Salt) H2SO4 + 2 NaOH = 2 H26 + Na2S04 (sodium 

sulphate). 
Certain of the less positive and less negative elements 
form oxides, which act as acids toward strong bases and as 
bases toward strong acids : — 

Sn02+H20 = SnO(OH)2 (metastannic acid), 
SnO(OH)2-f 2 H2S04= 3 H2O -f- Sn(S04)2 (stannic sul- 
phate), 
H2Sn03 -f 2 NaOH = 2 H2O + Na2Sn03 (sodium meta- 
stannate). 



2l8 GENERAL INORGANIC CHEMISTRY 

Sulphides 

The binary compounds of sulphur, known as sulphides, 
resemble those of oxygen. The affinity of sulphur, how- 
ever, for both positive and negative elements is less strong. 
Its compounds are less stable and the changes less numer- 
ous. All the sulphides, except those of the alkalies and 
alkaline earths, are insoluble in water. The sulphides of 
many positive elements are found in nature. In fact, this 
is the most general mode of occurrence of many of the ele- 
ments. The most common ores of metals are the oxides 
and sulphides. 

Formation of sulphides, i. By the direct union of the 
elements with sulphur : — 

Fe + S = FeS; CI2 + 83 = 01282. 

2. By the action of hydrogen sulphide, or soluble sul- 
phides, upon a solution of the salts of positive elements: — 

CUSO4 + H2S = I CuS + H2SO4, 
FeS04 + (NHj2S= | FeS -|-(NH4)2S04. 
Some of the sulphides are soluble in hydrochloric acid : — 
FeS + 2HCl = FeC]2 + H2S. 

The sulphides vary in their solubility in different sol- 
vents, and many have different colors. These facts are 
taken advantage of in detecting many of the elements, 
especially those of metallic character (qualitative analysis). 
For instance, they may be classified in three groups: — 

1. The sulphides soluble in water, hydrochloric acid, and 
ammonium hydroxide : alkaline sulphides, as Na2S, K2S5 ; 
alkahne earth sulphides, as CaS, BaS. 

2. Sulphides soluble in hydrochloric acid, but insoluble 
in water and ammonium hydroxide : FeS, CoS, NiS (all 
of which are black), ZnS (white), MnS (pinkish). 



HYDROXIDES 219 

3. Sulphides insoluble in hydrochloric acid: PbS, Ag2S, 
Hg2S, CuS (all of which are black), HgS (black, lighter 
until an excess of reagent has been added ; sometimes 
brilliant red), CdS, AS2S3, SnS2 (all yellow), 61283, SnS 
(both brown), Sb2S3 (orange-red). 

Hydrosulphides 

In striking analogy to the hydroxides we have the 
hydrosulphides, or sulphydrates, which may be looked 
upon as sulphides united to hydrogen sulphide: — 

Na20 + H20 = 2NaOH, CaO + H20 = Ca(0H)2; 
Na2S + H2S=2NaSH, CaS + H2S = Ca(SH)2. 

These compounds are doubtless formed when a solution 
of the alkaline and alkaline-earth sulphides is made in 
water. 

As in the case of the oxides, the sulphides may be base- 
forming or acid-forming. The hydrosulphides of strong 
positive elements are bases ; of these, only the hydrosul- 
phides of alkalies and alkaline earths are known. The 
hydrosulphides of the negative elements are acids, thio-acids. 
Very few of them are known in the free state, though their 
salts are known, for example : AS2S5, Sb2S3, SnSg, and 
H3ASS4, H3SbS3, H2SnS3. 

Selenium and Telhiritim do not form as stable com- 
pounds as oxygen and sulphur. A few of their compounds 
with electro-positive elements, as gold and silver, are found 
in nature and constitute important ores of those metals. 



220 GENERAL INORGANIC CHEMISTRY 

EXERCISES 

1. Write the equation, according to the first method, for pro- 
ducing (a) Yq^O^ from FeSs ; {p) SbgOg from vSb ; {c) TeOg from 
AuTcg. 

2. Do the same according to the second method for (^) SrO 
from SrCOa; {b) ZnO from Zn(0H)2 ; {c) AIO3 from A1(0H)3. 

3. Write the equation for preparing by the first method (a) P^Ss 
from P; (J?) HgS from Hg. 

4. Do the same by the second method for (a) AggS from AggNOg ; 
{b) B\2% from BiClg ; {c) ZnS from ZnClg ; {d) MnS from MnS04. 



CHAPTER XXXIV 

OXIDES, HYDROXIDES, SULPHIDES, AND HYDROSUL- 
PHIDES OF GROUP I 

Positive Series 

Ufi Na20 K2O Rb20 CS2O 
NagOa Rb202 CS2O2 



K2O4 Rb204 CS2O4 

LiOH NaOH KOH RbOH CsOH 

Li2S Na2S K2S ■ 

LiSH NaSH KSH 

The oxides and sulphides may be prepared by the first 
general method. 

The oxides are deliquescent, soluble, caustic, alkaline 
substances. They combine with water, generating heat to 
produce the hydroxides :— MgO + H2O = 2 MOH. The hy- 
droxides are used in place of the lower oxides, because 
they are more easily prepared and handled. The hydrox- 
ides absorb water and combine with carbon dioxide. 

LitJiium Oxide, \A^0. When heated, lithium burns in 
the air, giving a white oxide. The oxide is also produced 
by heating lithium nitrate. It is a white, crystalline mass, 
which slowly dissolves in water, forming LiOH. Lithium 
salts are too rare and expensive for common use. The 
most important salts are the carbonate and chloride. 

Sodium Monoxide, Na20. Sodium forms two oxides, 
Na202 being the second. When the metal is heated in the 



222 GENERAL INORGANIC CHEMISTRY 

air, the two are formed together. Also, 2 NaOH + Na^ "^ 
2 Na20 + H2. It is a grayish white mass, melting at a red 
heat. 

Sodium Hydroxide, sodium hydrate, caustic soda, NaOH, 
is prepared by two characteristic methods : — 

1. Na2C03+Ca(OH)2^|CaC03 + 2NaOH. 

2. By electrolysis, 

2 NaCl + 2 H20i^2 NaOH + f H2 +fCl2(Castner process). 
The hydrogen and chlorine are led away in separate pipes. 

Sodium hydroxide is a white solid which combines 
readily with the moisture and carbon dioxide of the air. 
The caustic may be melted, but it is decomposed at a 
very high temperature. NaOH forms a solid with water, 
NaOH, 2 H2O, at 0°, which melts at + 6°. Caustic soda is 
a corrosive poison, but has extensive use in the manufac- 
ture of soaps, in the decomposition of silicates in making- 
water glass, and so forth. 

Sodium Dioxide, Na202, is a slightly yellowish, deliques- 
cent substance, which readily absorbs carbon dioxide. On 
the addition of water, the solid is decomposed with the 
production of much heat and the formation of the hydrox- 
ide and oxygen : — NagOg + H2O = 2 NaOH -f- O. On ac- 
count of the production of oxygen it is extensively used in 
oxidizing and bleaching (oxone). When brought in con- 
tact with a combustible substance and a little water, rapid 
oxidation results, hence great care must be exercised in 
handling it. 

There seems to be another oxide, with the formula Na40, 
but little is known about it. 

Potassium Monoxide, K2O. Potassium also forms two 
oxides, the other oxide being K2O4, which is a dark yellow 
substance, possessing powerful oxidizing properties. On 
the addition of water so much energy is liberated that it 
becomes red-hot. At the same time a peculiar odor is noted. 



HYDROSULPHIDES OF GROUP I 223 

Potassium Hydroxide, potassium hydrate, caustic potash, 
KOH, is a deliquescent, very soluble substance which 
melts easily and may be volatilized. The water solution 
has a strong alkaUne taste and peculiar odor. It resem- 
bles caustic soda in other properties. It is soluble in 
alcohol. 

Rubidium and Ccesium form oxides and hydroxides 
analogous to those already mentioned. Little is known 
of them, however. 

Rnbidiicm Dioxide, Rb02, is a dark brown, crystalline 
substance which dissolves in water with a hissing sound 
and the evolution of oxygen. 

Amjnoniiim Hydroxide, ammonia hydrate, spirits of 
hartshorn, NH^OH, may be classed with this group, as it 
is strongly basic and resembles the alkalies. It is formed 
by the solution of ammonia in water. It has never been 
separated from the solution or prepared free from water. 
The solution gives off ammonia at ordinary temperatures. 
With acids it gives ammonium salts : — 

NH4OH + HClr> NH4CI + H2O. 

Sodium SiilpJiide, Na2S. When hydrogen sulphide is 
led into a solution of NaOH, this reaction takes place : — 

NaOH + H2S :±L Yi^O + NaSH. 

On the addition of an equal amount of the hydroxide 
sodium sulphide is formed : — 

NaSH + NaOH = H2O + Na2S. 

Sodium sulphide is also formed by heating sodium sul- 
phate and carbon together : — 

Na2S04 + 4 C :r> 1 4 CO + Na2S. 

It is often formed, with higher sulphides, when a sulphur 
compound is fused with sodium carbonate on charcoal. 



224 GENERAL INORGANIC CHEMISTRY 

Sodium sulphide is a colorless or slightly colored solid, 
very soluble in water, giving a colorless solution at first. 
It acquires a yellow color from decomposition and forma- 
tion of higher sulphides. It is used as a laboratory reagent, 
but is generally replaced by ammonium sulphide. 

The higher sulphides are : — Na2S, Na2S3, NagS^, and 
Na2S5. They are formed by the solution of sulphur in 
any of the lower sulphides. 

Sodium and Potassium Hydi'osulpJiides^ NaSH and 
KSH, are made according to the reaction given above; 
also, when H2S is passed over the heated metals : — 

2K + 2H2S=H2+2KSH. 

Ammoimim Siilphide, (NH^)2S, is formed by leading 
hydrogen sulphide into ammonium hydroxide until satu- 
rated and then adding an equal quantity of ammonium 
hydroxide. This is a colorless solution which dissolves 
sulphur, producing higher sulphides, the chief one being 
(N 1^4)255. A water solution of the polysulphide is yellow. 
Ammonium sulphide is used extensively in the laboratory. 

Negative Series 



CU20 


Ag^O 


AU2O 


CuOH 


AgOH 


AuOH 


CuO 


Ag202 




Cu(0H)2 




AU2O3 
Au(OH)3 


CU2S 


Ag,S 




CuS 








Cuprous Oxide, CU2O, is found in nature as red copper 
ore (cuprite). It may be formed by heating copper in 
oxygen insufficient to form the higher oxide. It is usually 



HYDROSULPHIDES OF GROUP I 225 

prepared indirectly (see below). The red powder is stable 
when dry, but when moist it absorbs oxygen. It gives 
glass a red color. 

Cicpric Oxide, CuO, also occurs naturally, but not so 
abundantly. It is prepared by heating the nitrate, car- 
bonate, hydroxide, or the metal, in the air or oxygen. It is 
a black solid, insoluble in water. It is stable even at 
higher temperatures, but loses its oxygen on being heated 
with reducing substances, such as hydrogen or carbon 
compounds. It colors glass green. It dissolves in acids, 
giving cupric salts : — 

CuO + H2SO4 -^ CUSO4 + H.p. 

Cuprous Hydroxide, CuOH, is obtained as follows : — 

CuCl -f NaOH:i^NaCl + CuOH. 

It is a yellow powder, easily absorbing oxygen from the 
air, becoming blue and changing into the higher hydrox- 
ide, Cu(0H)2. It is decomposed on heating with the 
formation of cuprous oxide. 

Cupric Hydroxide, Cu(0H)2, is prepared as follows : — 

CuSO^ + 2 NaOH ^ CuCOH)^ + Na2S04. 

It is a hght turquoise-blue jelly, insoluble in water. On boil- 
ing the freshly precipitated hydroxide, it loses its water and 
is partially changed into the oxide : — 

Cu(OH)2r^CuO+H20. 

Substances containing hydrogen and oxygen as hy- 
droxyls, as a rule, decompose on heating, with the elimina- 
tion of water (see general methods). The degree of heat 
necessary to bring about this change is characteristic for 
each substance. Elements weak in chemical affinity do 
not hold the hydroxyl groups as firmly as the more active 



226 GENERAL INORGANIC CHEMISTRY 

elements. The hydroxide of copper begins to decompose 
below + 1 00°. With some substances it is not neces- 
sary to remove the water from the sphere of the reaction. 
For example, if we boil CuOH suspended in water, the 
hydroxide is decomposed : — 

2CuOH^Cu20 + H2O. 

Cupric hydroxide, when dry, is not so easily decomposed. 
If the fresh precipitate is dissolved in ammonium hydroxide, 
it forms a deep azure-blue solution. This solution will dis- 
solve cellulose. Cupric hydroxide is not dissolved by sodium 
hydroxide unless certain organic substances, as tartrates, 
glycerol, and so forth, are present. If they are present, a 
deep blue liquid is obtained. If a reducing substance, like 
grape sugar, is added to the liquid, Cu(OH)2 is reduced 
to CuOH, which separates. On boiling, the red Cu^O is 
formed. These facts are utilized in determining the amounts 
of reducing substances in urine, for example, sugar. 

Silver Oxide, Kg^O. Silver does not combine with 
oxygen when heated in the air. It is prepared by precipi- 
tating a solution of silver nitrate by an alkaline hydroxide. 
We should expect AgNOg+NaOH^ AgOH + NaN03, 
but this hydroxide does not exist at ordinary tempera- 
tures. The moist oxide acts in many ways like an hydrox- 
ide. It is even less stable than cuprous hydroxide, being 
decomposed into silver oxide and water at — 40°. It is an 
almost black powder, insoluble in water, and is alkaline in 
reaction. It absorbs carbon dioxide from the air. It is 
reduced by hydrogen at +100° and decomposed by heat- 
ing to a temperature of -f 250°. Ozone oxidizes silver 
directly. 

Argeiitoits Oxide, silver suboxide, Ag^O, is said to be 
formed by the reduction of silver salts. Silver Dioxide, 



HYDROSULPHIDES OF GROUP I 22/ 

Ag202, is foraned by th-e action of ozone upon silver. The 
important silver salts are formed after the type, Ag20. 

Gold Monoxide, aurous oxide, AU2O. Gold also forms 
auric oxide, AU2O3. These are both prepared indirectly. 
When cold dilute potassium hydroxide is added to aurous 
chloride, the former oxide is produced as a violet colored 
powder which is decomposed at + 250°. It is readily 
decomposed by alkalies, but not much affected by the 
acids. 

Gold Trioxide, auric oxide, AU2O3, a dark, insoluble 
powder, is obtained by heating the hydroxide to +100°. 
It is decomposed by further heating. 

Gold Hydroxide, auric hydroxide, Au(0H)3, is best 
prepared by heating gold trichloride with an excess of 
magnesia. If prepared by an alkaline hydroxide, some of 
the alkali is retained. It is a brown powder, decomposing 
in the light or on heating to + 100°. It is a weak base, 
forming auric salts with strong acids. It readily loses one 
molecule of water, formic auric acid, AuO,OH, which re- 
acts with strong bases to give aurates : — 

AuO,OH + NaOH = H2O + Na AUO2. 

By the action of ammonia upon moist silver oxide or 
upon gold hydroxide, peculiar compounds are obtained ; 
these are respectively called "fulminating silver," Ag20, 
2 NH3, and "fulminating gold." Both are explosive. 

The sulphides of copper and silver are closely analogous 
to the oxides. Several of them occur in nature, as copper 
glance, CU2S ; blue copper, CuS ; silver glance, Ag2S. 
Chalcopyrite, CU2S, Fe2S3, is one of the most important 
ores of copper, as is also bornite, 3 CU2S, Fe2S3. There is 
some question as to the existence of gold sulphide. 



228 GENERAL liNORGANIC CHEMISTRY 

EXERCISES 

1. Why should the hydrogen and chlorine be led away in sepa- 
rate pipes in the Castner process ? 

2. Write the equations for the preparation of colorless ammo- 
nium sulphide. 

3. Write the reactions which take place when silver sulphide 
(AgaS) is roasted. 



SrO 


BaO 


Sr(0H)2 


Ba(OH)2 


SrO^ 


Ba02 


SrS 


BaS 


Sr(SH)2 


Ba(SH)2 



CHAPTER XXXV 

OXIDES AND SULPHIDES OF GROUP II 

The type formulas for this group are, MO, MS, M(OH)2, 
and M(SH)2. The members of the positive series also 
form a dioxide according to the type MO2. Two members 
of the negative series form oxides according to the type 

M2O. 

Positive Series 

BeO MgO CaO 

Be(0H)2 Mg(OH)2 Ca(OH). 

Mg02 Ca02 

BeS MgS CaS^ 

Ca(SH)2 

Both of the general methods are appUcable for the prep- 
aration of the oxides and sulphides. The oxides of the 
positive series are basic and caustic, but are less caustic 
than the alkalies. The oxides of the positive group are not 
found in nature. An impure magnesium hydroxide is 
found, however. 

Magnesium Oxide, magnesia, MgO, may be obtained by 
heating the carbonate, when it is called '* magnesia usta." 
It is also prepared by the ignition of metallic magnesium 
in the air. It is a very hght, white, tasteless powder which 
melts without decomposition. It slakes very slowly with 
water, forming — 

Magnesium Hydroxide, Mg(0H)2, which gives an alka- 
line reaction with litmus paper. It is usually prepared by 
treating a soluble salt with a soluble base : — 

MgCl2 + 2 NaOH -±_ \ Mg(0H)2 -f 2 NaCl. 
229 



230 GENERAL INORGANIC CHEMISTRY 

When this is suspended in water it is used medicinally as 
*' milk of magnesia." It neutralizes acids. When ignited, 
it is converted into the oxide and is then used for the 
lining of crucibles and converters. 

Calcium Oxide, quick-lime, CaO, is obtained by heating 
marble or limestone according to processes which may be 
continuous or intermittent. The rock shrinks about fifteen 
per cent, but loses about forty per cent, in weight. 

CaC03:;tCaO + C02. 

Lime is a white mass which fuses at + 2500°. When 
heated by an oxyhydrogen flame, which has a tempera- 
ture of + 2100°, it produces a brilliant light known as the 
Drummond or lime light. Lime is a strongly caustic sub- 
stance. It combines with water with the generation of 
much heat (slaking) to form — 

Calcium Hydroxide, slaked lime, Ca(0H)2 : — 

CaO + H20:^Ca(OH)2. 

Calcium hydroxide is mildly caustic. It is a white powder, 
slightly soluble in water, i : 760. The perfectly clear solu- 
tion is known as '' lime-water " and is used in medicine. 
It has a strongly alkaline reaction, and neutralizes acids. 
When calcium hydroxide is stirred up with water, it is 
called ''milk of lime." Lime is a very important material, 
extensively used in commerce. It is always more or less 
impure. When the amount of impurities is small, it is 
known as "fat lime"; when the impurities are high in 
percentage, "poor lime." 

Lime is used in making mortar. One part by weight of 
lime is slaked with from three to six parts of water. If 
this milk of Hme is allowed to dry, it forms a film which 
on further drying cracks, owing to shrinkage. If this milk 



OXIDES AND SULPHIDES OF GROUP II 23 1 

of lime is diluted, as it \v«re, by the addition of sand (three 
to four parts), the shrinkage is largely overcome. The 
cream forms a coating over the grains of sand and on dry- 
ing causes what is known as the setting of mortar. Grad- 
ually the calcium hydroxide absorbs carbon dioxide from 
the air, bringing about a hardening of the mortar, due to 
the formation of calcium carbonate : — 

Ca(0H)2 + CO2 z± CaCOgH- H2O. 

It is thought also that some of the sand after a long period 
of time combines with lime to form a silicate according to 
the following reaction : — 

Ca(0H>2 -h SiO, = CaSiOg -f H^O. 

When hme is left exposed to the air, the moisture of the 
air slakes it, and the carbon dioxide of the air is fixed by 
the hydroxide formed. The product is then known as 
"air-slaked lime" and is useless for making mortar. 

Calciinn Dioxide^ Ca02, is prepared by adding hydrogen 
dioxide to lime-water. It usually crystallizes with 8 HgO. 
When heated or brought in contact with organic matter, 
it gives up oxygen. Calcium dioxide is used in dentistry. 

The corresponding strontium compounds are similar to 
those of calcium. 

Barium Oxide, baryta, BaO, is made by heating a salt of 
barium with a volatile acid radical. Barium Hydroxide 
Ba(0H)2 is made by the following reaction : — 

BaCOg + C + H2O (steam) = 2 CO + Ba(0H)2. 

Barium hydroxide is comparatively soluble in water, be- 
ing less soluble in hot than in cold water, which is unusual. 

Barium Dioxide, Ba02, is prepared by heating BaO in a 
stream of dry oxygen or by heating the hydroxide in the 
air at -f 400°. If the temperature is raised to + 700°, the 



232 GENERAL INORGANIC CHExMISTRY 

oxygen is given off; if the temperature, is lowered, the 
oxygen is taken up again. It is a grayish, porous body, 
more fusible than BaO. It combines with water to form 
a hydrate, Ba02, 8 H^O. It is. used mainly for the prepara- 
tion of hydrogen dioxide. 

The Sulphides of this series are formed by the action 
of carbon at high temperature on the corresponding sul- 
phates : — Q.^^Q^ + 4 C = 4 CO + CaS. 

The sulphides have the property of glowing in the dark 
after exposure to sunshine or strong light. They are the 
chief constituents of '' luminous paint." The pure sulphides 
do not possess this property. Calcijini Sulphide, CaS, is 
slightly soluble in water. It is a waste product in the 
Le Blanc soda process. The sulphur is partly recovered 
from it now. Barium Sulphide, BaS, is more soluble. 

When treated with hydrogen sulphide, the sulphides are 
changed into the hydrosulp/iides : BaS + H2S = Ba(SH)2, 
analogous to BaOH + H2O = Ba(0H)2. 

Negative Series 

~ — Cd20 Hg20 

^ CdOH (HgOH) 

ZnO CdO HgO 

Zn(OH)2 Cd(OH), Hg(OH)2 

Hg02 

Hg2S 



ZnS CdS HgS 

These oxides differ from the former by not slaking with 
water and in being less basic. The hydroxides are obtained 
by precipitation and are less stable. 

Zinc Oxide, ZnO, occurs as zincite, or red zinc ore. 
The color is due to impurities, for the pure oxide is white. 



OXIDES AND SULPHIDES OF GROUP II 233 

It may be prepared by .burning the metal (zinc white). 
For medicinal use the carbonate is heated. It is a heavy 
white powder, yellow when hot, insoluble in water. It is 
used in making white paint, which does not darken when 
in contact with hydrogen sulphide. 

Zinc Hydroxide, Zn(0H)2, is obtained as a white powder 
by precipitating and drying the precipitate obtained in the 
following reaction : — 

ZnSO^ + 2 NaOH = Na2S04 + Zn(0H)2. 

This precipitate is insoluble in water. It loses water on 
being heated and is converted into the oxide. It is soluble 
in acids and alkalies : — 

Zn(0H).2 4- 2 HCl:r>2 H^O + ZnCl^ ; 

Zn(0H)2 + 2 NaOHz±2 H2O + Na.2Zn02 (sodium zinc- 
ate). 

Cadviium Oxide, CdO, is a brown powder, obtained by 
burning the metal in the air. The Hydroxide, Cd(0H)2, is 
a white precipitate, similar to the zinc compound. It is 
decomposed at + 300°. It absorbs carbon dioxide from 
the air. 

Cadmous Oxide, Cd20, and its corresponding hydroxide, 
CdOH, are also known. 

Mercinviis Oxide, Hg20, is obtained by the action of 
alkalies on mercurous compounds : — 

2 HgNOg + 2 NaOH ^ 2 NaNOg + H2O + | Hg20. 

The black insoluble powder, under the influence of light 
or moderate heat, undergoes the following change : — 
Hg,0 = Hg + HgO. 

Mercuric Oxide, HgO, is the red oxide. In early times 
this was called ''red precipitate," or *' precipitate per se." 
It is prepared by heating mercury in the air for a long 
time just below its boiling point or by heating the nitrate. 



234 GENERAL INORGANIC CHEMISTRY 

It is a very heavy, red, insoluble solid, with an alkaline re- 
action. It is decomposed by heat : — 2 HgO :^ 2 Hg + O^. 
It may also be prepared by precipitating a solution of a 
mercuric salt with an alkah, when it forms an orange-yellow 
powder: — 

Hg (N03)2 + 2 NaOH :± 2 NaNOg + H^O + HgO. 

The hydroxides of both of these oxides do not exist at 
ordinary temperatures. At — 42°, HgOH is known. Note 
the similarity here with copper and silver, regarding the 
stabihty of the hydroxides, and the analogy to the former, 
regarding the valence of the elements. 

The S It Ip hides of the Negative Series are Zinc Sulphide, 
sphalerite, or blende, ZnS ; Cadmium Sulphide, greenockite, 
CdS; and MerciLvic Sulphide, cinnabar, HgS. These consti- 
tute the chief ores of these metals. Mercuric sulphide is 
made by subliming a mixture of the elements : — Hg -|- S = 
HgS (red) ; or by precipitation with HgS : — HgClg + 
HgS :± 2 HCl -h HgS (black). 

The precipitate is black, but is converted into the red 
form by sublimation. It is then known as vermilion and 
is used as a pigment. 

Mercurons Sulphide, HggS, has been prepared by the 
action of concentrated sulphuric acid upon mercury at 
ordinary temperatures for a long period of time. 

EXERCISES 

1. How much lime is theoretically obtainable from 9 tons of 
limestone which is 97 percent pure? 

2. How much barium dioxide is necessary to make 5 pounds 
of a 4 per cent solution of hydrogen dioxide? 

3. How much of a tenth-normal hydrochloric acid solution is 
necessary to neutralize 3 grams of strontium hydroxide? 



CHAPTER XXXVI 
THE OXIDES AND SULPHIDES OF GROUP III 

The type oxide of this group has the formula M2O3. 
These oxides are widely distributed in nature, but not in 
large quantities. They are very stable and are less basic 
than the oxides of the preceding group. They constitute 
the basis of what are known as the " earth oxides." 

Boron Trioxidc, boron anhydride, B2O3, may be obtained 
by burning boron in the air, but it is more usually prepared 
by heating the hydroxide, B(0H)3, which occurs in nature. 
It is a white hygroscopic solid which melts without de- 
composition. It volatilizes at a white heat and unites with 
water to form boric acid. Many metallic oxides dissolve 
in boron oxide, when it is fused, giving glasses with char- 
acteristic colors. 

Boron Hydroxide, orthoboric acid, boric acid, boracic 
acid, B(0H)3, is formed by decomposing borax (Na2B407, 
10 H2O) with a mineral acid, when it is obtained as fine 
crystals. It is found dissolved in certain lakes of Tuscany, 
Nevada, and California. It is a weak acid, the salts of 
which are found in the same places. On passing steam 
through a solution in which it is present, it is volatilized. 
It acts similarly with the vapor of alcohol, which burns 
with a green flame when boron hydroxide is present. 
When fused with salts of a mineral acid, as calcium sul- 
phate (CaSO^), the mineral acid is replaced ; whereas a 
salt of orthoboric acid in a water solution is decomposed 
by a mineral acid. 

235 



236 GENERAL INORGANIC CHEMISTRY 

Metaboric Acid, BO (OH), is obtained by heating ortho- 
boric acid to + 1 00°. It is a white powder which, on 
heating with the positive elements of the first two groups, 
forms salts, metaborates. 

Tetraboric Acid, 6405(0^1)2. When orthoboric acid is 
heated a long time at + 140'', this reaction takes place : — 

4B(OH)3 = 5H,0 + B,05(OH),. 

This acid forms stable compounds with many metals, 
giving borates, the most important one being — 

Borax, di-sodium tetraborate, '^2.^^)^^, 10 H2O. It occa- 
sionally occurs in solution in springs and lakes, as in 
Nevada, California, and Central Asia. The crude form, 
in which it is marketed, is called "tincal." It is white, 
crystallizing in monoclinic prisms. It is very soluble in 
water; at + 30°, i : 14; at + 100°, i \\. Its water solution 
is feebly alkaline. Sometimes it crystallizes in octahedra 
at +70°, with 5 H2O. It loses its water on heating and 
swells up (intumesces). At + 850°, all the water is ex- 
pelled, and there results a glassy mass, called borax glass 
{^2L^f^r^\ which possesses the property of dissolving 
many metallic oxides, forming colored glasses. It is used 
in soldering metals, in enamel work, in ceramics, in silk 
manufacture, and as a cleansing agent. 

Borax and boric acid are antiseptic and are often used 
as preservatives of food. The use of such preservatives, 
however, is objectionable. 

Boracite, 2 MggBgOjg, MgCl2 (Stassfurt), Colemanite, 
Ca2BgOii, 5 H2O (Mono Lake), and HCa(B02)3, 2 H2O, 
are minerals from which much boric acid is prepared. 

Ahunimt7n Oxide, alumina, AI2O3, occurs nearly pure in 
hexagonal crystals in a number of minerals and precious 
stones, as ruby, sapphire, corundum, emery, and so forth. 



OXIDES AND SULPHIDES OF GROUP III 237 

They have an average specific gravity of 3.9 and are next 
to the diamond in hardness. Alumina may be prepared 
by heating the hydroxide or by precipitation of an alkahne 
aluminate by means of carbon dioxide : — 

2 NaAlO.^ + CO2 = I A1203 + Na2C03. . 

Obtained in this way it is a white powder which may be 
crystalHzed by melting and allowing it to cool under pres- 
sure (alundum). In this manner synthetic gems are made. 
This form is insoluble in water, but is soluble in strong 
acids, provided it has not been previously heated too 
strongly. After intense ignition it is very hard and is 
used for polishing glass and metal. It is very stable and 
is not decomposed at the highest temperature so far 
obtained. It dissolves in fused cryolite. In this condition 
it may be decomposed by an electric current, the metal 
separating at the negative pole (process of Hall). 

Ahimininn Hydroxide, Al(OH)3. Several hydroxides oc- 
cur naturally : hydrargillite, A1(0H)3, diaspore, AIO(OH), 
and bauxite, (AlFe)20(OH)4. The type is prepared as a 
gelatinous precipitate by this reaction : — 

Al2(S04)3 + 6 NH,OHl^3 (NH4)2SO, H- |2 Ai(0H)3. 

Freshly precipitated, it is easily dissolved in acids, but 
on long standing in water it becomes less soluble. It is 
used for the purification of water, because it has the power 
of removing not only suspended matter but even dissolved 
material. The jelly enmeshes bacteria and as it settles 
removes them. It is also used for fixing colors (mordant) 
and for tanning. For this purpose usually a salt that is 
readily decomposed or hydrolysed, as the acetate, is used. 
When prepared in a cold solution, it separates as a gelatin- 
ous precipitate, which may be filtered and purified by wash- 
ing with water. If the purified body is added to a solution 



238 GENERAL INORGANIC CHEMISTRY 

of aluminum chloride, it dissolves. The, form is called a 
hydros ol. If the solution is heated, the jelly separates out. 
It is then called a hydro gel. 

In studying osmosis, we learned that many substances 
pass through a membrane. These substances, as a rule, 
may be had in a crystalline condition; therefore, for many 
years those substances which would pass through a mem- 
brane when in solution were called ciystalloids. A solid, 
like the gelatinous aluminum hydroxide, does not pass 
through a membrane. If we place a solution of the alumi- 
num hydroxide in aluminum chloride in water (hydrosol) in 
an osmotic cell and run water in for some time, it will be 
observed that the crystalloid aluminum chloride passes 
through the membrane, leaving a perfectly clear solution 
behind. If the latter is heated, a jelly separates. That is 
to say, the hydrosol does not pass through the membrane. It 
is devoid of crystalline form. Such a substance is spoken 
of as a colloid. This illustrates a general principle of very 
wide application, known as dialysis. Very recently, how- 
ever, it has been learned that some colloids in certain solu- 
tions will pass through particular membranes, so the dis- 
tinction no longer holds (Kahlenberg). Also it has been 
learned that some crystalloids in certain solutions may be 
separated from other crystalloids by dialysis, when special 
membranes are used, and certain colloids may be separated 
from other colloids in the same manner. These facts, not 
yet thoroughly explained, are of fundamental importance, 
for under normal conditions of health those substances 
which constitute food of necessity pass into the blood by 
dialysis and are thus distributed throughout the animal 
system. At the same time the blood acquires the waste 
products of the tissues, and in its course comes into contact 
with various secretory organs of the body, the kidneys, for 



OXIDES AND SULPHIDES OF GROUP III 239 

example, which in turn by dialysis remove certain sub- 
stances and discharge them from the body. 
, Ahiniiiiatcs. Toward strong bases aluminum hydroxide 
acts as an acid ; for example, 

A1(0H)3 + NaOH - 2 H2O + NaA102. 

The resulting compounds are derivatives of meta-alu- 
minic acid, AIO(OH). Several salts of this are found in 
nature ; for example, spinel, Mg(A102)2 ; chrysoberyl, 
Be(A102)2; and gahnite, Zn(A102)2- Sodium aluminate 
is produced in preparing alumina from bauxite and is 
used as a mordant. 

The other oxides of this group are not important. Lan- 
thanum forms La203 and La205. Thallium forms TI2O 
and T1203. 

Sulphides 

The Sulphides of Group III are formed only in the dry 
way, as they are decomposed by water: — 

A12S3 + 6 H2O = 2 A1(0H)3 -h 3 H2S. 

We would expect a soluble sulphide to precipitai:e the 
sulphide according to this reaction : — 

Al2(SO,)3 + 3 (NH,),S = 3 (NH,)2SO, + IK\%. 

But, as shown in the first reaction, the aluminum sulphide 
is decomposed; so we write what actually takes place, as 
follows : — 

Al2(SO,)3 + 3(NH,),S + 6 H^O 

=2-2 Al(OH)3 + 3 (NH,)3S04 + 3 HjS. 



240 GENERAL INORGANIC CHEMISTRY 

EXERCISES 

1. Write the reaction for making orthoboric acid from borax, 
using hydrochloric acid. 

2. Make a diagram showing the relationship among the acids of 
boron. 

3. Complete this reaction : — 

La,(S04)3 + 3 (NH4)2S + 6 HsOz^ 



CHAPTER XXXVII. 

OXIDES AND SULPHIDES OF GROUP IV. CARBONATES OF 

GROUP I 

The type oxide is MO2. Carbon Dioxide and Monoxide 
have been studied. 

Acid and Basic Salts. When carbon dioxide is dissolved 
in water, we have formed the hypothetical carbonic acid, 
H2CO3. Either one or both of the hydrogen atoms may 
be replaced by an electro-positive element or radical. 
When all the acid-hydrogen is thus replaced, we have 
what is known as a normal salt, as Na2C03. When only 
a portion of the hydrogen is replaced, we have what is 
known as an acid salt, NaHCOg. If we take a base com- 
posed of an electro-positive element or radical, containing 
two or more hydroxyls, as, for example, Bi(OH)3, we may 
replace all of the hydroxyls by electro-negative elements or 
radicals and obtain a normal salt, as BiClg. If only a por- 
tion of the hydroxyls is replaced, we have a basic salt, 
Bi(0H)2CL The salts of carbonic acid are called carbon- 
ates and we may appropriately study them at this point. 

Carbonates of Group I 

The carbonates of the positive members of this series are 
usually white crystalline solids, soluble in water, having an 
alkaline reaction and remaining stable up to the tempera- 
ture of melting. The normal carbonates have the formula 
M2CO3, and the acid carbonates, or dicarbonates, the 
formula MHCO3. 

241 



242 GENERAL INORGANIC CHEMISTRY 

Sodiiun Carbonate, soda, laundry soda,. Na2C03, occurs 
naturally as natrona, dissolved in certain lakes of Egypt, 
South America, and the United States. It is also obtained 
from sea-weeds, the burned ashes of which were called 
** kelp " or "' varec." The demand for it was so great that 
other processes were devised. Its manufacture is one of 
the most important industries and is known as the Alkali 
Industry. 

There are three general processes for the preparation of 
sodium carbonate. They are given in some detail, as they 
illustrate the practical economic application of important 
principles. All of them start from sodium chloride, the 
cheapest and most abundant source of sodium and chlorine. 

I. The Le Blanc process (1794): — 

2 NaCl + H2S04=:> ^2.,^0^ + f 2 HCl. 

The hydrogen chloride was allowed to escape in the 
air, until complaints of the injury produced on vegetation 
brought about the enactment of laws in England (Alkali 
Act, 1863, et seq.) which required its absorption. Its 
saving later constituted a large part, if not all, of the profit 
by this method. The sodium sulphate is mixed with car- 
bon (ground charcoal or coke) and heated in a "balling" 
furnace to produce the sulphide of sodium : — 

Na2S04 + 4 C7± Na^S -F t4 CO. 

This in turn is treated with water and limestone : — - 

Na2S + CaCOgi^ Na2C03 + CaS. 

Sodium carbonate is dissolved in water and purified by crys- 
talUzation, separating as Na2C03,io HgO, or what is com- 
monly called "sal soda." The sulphur is now recovered 
from the sulphide, which for years was a waste product. 



CARBONATES OF GROUP I 243 

It will be observed here that both the sodium and chlorine 
are saved, but sulphuric acid and limestone are used up. 

2. The Solvay, or ammonia-soda process (1863) depends 
upon the formation of ammonium hydrogen carbonate, 
when ammonia and carbon dioxide are brought together 
m water : — ^p^^ _^ j^^O + CO.^Z^ NH4HCO3. 

This, in contact with sodium chloride, under pressure at a 
temperature not above +40°, gives the following reaction: — 

NH4HCO3 + NaCl^NaHC03 + NH^Cl. 

The sodium hydrogen carbonate, called sodium bicarbon- 
ate or dicarbonate, is much less soluble than the chloride, 
hence may be separated by evaporation and cooling. The 
crystals are then gently heated : — 

2 NaHC03 :^ Na2C03 + H2O + CO2. 

The ammonia is expensive and must be used over again ; 
it is recovered by the following reaction : — 

2 NH4CI -h CaO ^ 2 NH3 + CaC]2 + H2O. 

In the process all the sodium is obtained, but the chlo- 
rine is lost. 

3. The Castner process (1888) depends upon the forma- 
tion of sodium hydroxide, by electrolysis, and its conversion 
into the carbonate, by treatment with carbon dioxide, which 
is had in abundance from the fermentation industries : — 

NaCl = Na + Cl; 
2 Na + 2 H2O i^ 2 NaOH + H2 ; 
2 NaOH + C02r^Na2C03 + H2O. 

As the carbonate may be made from the dicarbonate, so 
the reverse change may also take place : — 

Na2C03 + H2O + CO2 :± 2 NaHCOg. 



244 GENERAL INORGANIC CHEMISTRY 

Everything is saved. The cost essentially depends upon 
the price of the electric current used. The chlorine is 
partly absorbed by slaked lime to make '' bleaching pow- 
der " and partly burned in the hydrogen generated to make 
very pure hydrochloric acid. 

Na2C03, 10H2O crystallizes in raonoclinic prisms which 
crumble on exposure to the air on account of efflores- 
cence. The crystals melt at + 50°. Sodium carbonate 
may also be had with 7 or 2 molecules of water. It is 
soluble in water; 100 parts dissolve 7 at 0° and 52 at 
+ 38°. It is less soluble at a higher temperature, due doubt- 
less to the formation of the lower hydrates, which are not 
as soluble as the decahydrate. All of the water is lost on 
heating. Its solution has a strong alkaline reaction and 
taste. It is known as soda ash, sal-soda, and washing 
soda, and is used in enormous quantities for making glass, 
paper, soap, and so forth. 

Sodium Dicarbonate, or sodium hydrogen carbonate, 
NaHCOg, is less alkaline and less soluble in water. It is 
decomposed on heating according to the reaction given. 
It is called cooking soda, and has many uses on account of 
the large amount of carbon dioxide contained in it. It is 
one of the chief constituents of baking powder. It effer- 
vesces when mixed with certain substances on account of 
the evolution of carbon dioxide : — 

NaHCOg + HCl zt NaCl + Hp + f CO2 ; 
6NaHC03 + Al2(S04)3:^|2Al(OH)3 + t6C02 + 3Na2S04. 

The use of aluminum compounds in baking powder is ob- 
jectionable. 

Potasshnn Carbonate, K2CO3, is obtained by leaching the 
ashes of land plants. 1000 parts of wood give 3.5 to 28 
parts of ashes, or from 0.45 to 4 parts of "potashes." It 



CARBONATES OF GROUP I 245 

is also obtained by leaching the ashes of sugar beets, from 
molasses residues, and in the purification of sheep suint. 
The crude material is purified by recrystallization and is 
then called ''pearl-ash." It is usually a granulated, deli- 
quescent powder, melting at + 890°. The impure form 
contains much water and is called ''potash alkaH." Re- 
cently potassium carbonate has been made from potassium 
chloride by a modified Solvay process, trimethylamine, 
N(CH3)3, being substituted for ammonia. 

LitJiiiLiii Carbonate, Li^COg, is the only one of these car- 
bonates that is not readily soluble in water. 

Animoniiun Ca7'bonatc, (NH4)2C03, is known as "smell- 
ing salts." 

Salts of Percarbonic Acid, H2C20g, are obtained by elec- 
trolysis of the acid carbonates. Potassium Percarbonate is 
obtained by electrolyzing a solution of potassium carbon- 
ate cooled to — 15°, when a slightly blue colored powder, 
K2C2OQ, separates. When heated to from + 200° to -h 300°, 
it is decomposed into the carbonate and oxygen. Oxygen 
is also given off by the aqueous solution at -f- 45°. It is 
a powerful oxidizing agent, similar to hydrogen dioxide, 
and many dyes are bleached by it. 

Carbonates of the Negative Series of Group I 

These differ very much from the alkaline carbonates in 
solubility, stability, and the mode of preparation. 

The Copper Carbonates occur in nature as green mala- 
chite, CuCOg, Cu(OH)2, and blue azurite, 2 CuCOg, Cu(0H)2. 
These carbonates are formed by the action of carbon dioxide 
and water upon copper or by the precipitation of copper 
salts with an alkaline carbonate. Only the basic carbon- 
ates are known. They are insoluble in water and are 
readily decomposed by heat. 



246 GENERAL INORGANIC CHEMISTRY 

The normal Carbonate of Silver is formed by precipita- 
tion : — 

2 AgNOg + NaaCOg :± \ Kgf.0^ + 2 NaNOa- 

EXERCISES. 

1. Tabulate the materials used, saved, and wasted in the three 
processes mentioned for the manufacture of sodium carbonate. 

2. How much sodium hydrogen carbonate should two tons of 
sodium chloride yield? How much hydrogen chloride? 



CHAPTER XXXVIII. 
CARBONATES OF THE REMAINING GROUPS 

Many of the carbonates of Group II (type MCO3) occur 
naturally. Most of them may be prepared by precipitation 
with a soluble carbonate. When made thus, they are white 
powders, nearly insoluble in water. They are also pre- 
pared by the action of carbon dioxide upon the oxide or 
hydroxide. They are decomposed by acids and heat. 

Magnesium Carbonate, MgCOg, occurs naturally as mag- 
nesite, or combined in varying proportions with calcium 
carbonate as dolomite (a'MgC03, jCaCOg). On precipi- 
tating a solution of magnesium sulphate with sodium car- 
bonate, a hydrated basic carbonate [3 MgCOg, Mg(0H)2, 
4 H2O] is formed. It is called ''magnesia alba" and is 
used medicinally. The composition varies with the tem- 
perature, concentration of solution, and other conditions of 
precipitation. Magnesium carbonate is a white powder 
insoluble in water. It dissolves in water charged with 
carbon dioxide, due to the formation of an acid carbonate, 
Mg(HC03)2. On heating to -f 300°, the carbonate decom- 
poses : — MgCOa = MgO -f- \ CO2. 

Calcinm Carbonate, CaCOg, occurs in nature in many 
forms and with many names : aragonite, which is the 
rhombic crystalline form, sp. gr. 3 ; calcite, or Iceland spar, 
hexagonal and rhombohedral, sp. gr. 2.7 ; and some calcites 
which are amorphous and others which are pseudo-crystal- 
line. The granular form is marble. Limestone, coral, 

247 



248 GENERAL INORGANIC CHEMISTRY 

shells, chalk, and marl are forms of calcium carbonate 
with more or less impurities. When prepared as follows, 
CaCl2 + Na2C03 = 2 NaCl + j CaCOg, it is called " precip- 
itated chalk," and is used medicinally and for polishing. 
On passing COg through lime-water, a precipitate is formed 
at first : — Ca(6H)2 + CO2 = j CaCOg + Hfi. On con- 
tinuing the passage of the gas, the precipitate dissolves, due 
to the formation of the acid carbonate : — CaCOg + H2O 
+ CO2 = Ca (11003)2. 1000 parts of water at +15° will 
dissolve 0.385 gram of this substance. Its solution gives 
what is known as temporary hardness to water, for, on heat- 
ing, the carbon dioxide is given off and CaCOg is formed, 
separating as a fine powder. When waters charged with 
the acid carbonate are exposed to the air, the change takes 
place very slowly. The carbonate separates as compact 
crystals, forming stalactites and stalagmites. When heated 
to a red heat, limestone breaks up : — CaCOg :^ CaO 
+ f CO2. This decomposition takes place only to a limited 
extent when the carbonate is heated in a sealed tube, for the 
pressure exerted by the gas in the tube becomes equal to 
that of the carbon dioxide which tends to escape from the 
carbonate. 

Strontium Carbonate, strontianite, SrCOg, is decomposed 
at + 1000°. Barium Carbonate, witherite, BaCOg, is de- 
composed at -f 1400° to + 1500°. Their properties are 
very similar to those of calcium carbonate. However, as 
the molecular weight increases, the bodies are more insol- 
uble and more difficult to decompose on heating. 

Of the negative series, Zinc Carbonate, ZnCOg, is found 
in nature as calamine, which is an important zinc ore. 
Basic zinc carbonates are also known. 

The elements of smaller atomic weights in Group III 
show little tendency to form carbonates. When we would 



CARBONATES OF THE REMAINING GROUPS 249 

expect aluminum carbonate to be formed, it is decomposed 
by the water present, forming the hydroxide as in the case 
of the sulphide : — 

2 AICI3 + 3 Na2C03 + 3 H2O 

= 2 Al (0H)3 + 6 NaCl +t 3 CO2. 

Lanthamnn Oxide, LagOg, however, combines readily 
with carbon dioxide to form the carbonate. It is found in 
nature as lanthanite, La2(C03)3. 

No definite carbonates of the positive series of Group IV 
are known. This statement applies also to the negative 
series, with the exception of lead. This carbonate occurs 
naturally as cerussite, PbCOg. Carbonic acid, H2CO3, is 
very unstable, readily -breaking up, CO2 being given off. 
Many of the salts of this so-called acid possess this prop- 
erty, and are readily decomposed by water, with loss of 
more or less of their carbon dioxide. Basic carbonates 
result. This is particularly true of artificially prepared lead 
carbonate, 2 PbCOg, Pb (0H)2, which is called white lead. 

The historic Dutch process for the manufacture of. 
white lead depends upon exposing rolls or buckles of thin 
lead in earthenware pots. The rolls are supported on 
false, perforated bottoms, below which is vinegar, or dilute 
acetic acid. These are covered with boards, upon which 
are placed either manure or spent tan bark, and then 
another row of boards, and so on until the room is filled. 
They are left so for several weeks. The heat generated 
by the fermentation of the manure partially volatiHzes the 
acetic acid, which forms a basic lead acetate. This in turn 
is acted upon by the carbon dioxide, resulting from the fer- 
mentation, and forms basic lead carbonate. The process 
takes place from the surface and gradually works into the 
metal. When the action is completed, the rolls are taken 



250 GENERAL INORGANIC CHEMISTRY 

out and the carbonate is removed from the lead and then 
ground. The reactions expressing these changes are : — 

3 Pb {C^Hfi^\ + 3 Na^COg = 3 PbCOg + 6 NaQHgO^, 
3 PbC03 + H2O = Pbg (003)2, (OH)2 + CO2. 

White lead is the basis of most paints. It is blackened 
by hydrogen sulphide, due to the formation of PbS. 

With regard to the carbonates of the remaining groups, 
it may be said that carbon dioxide appears to form no 
combinations, except with certain elements of the positive 
series, or some having high atomic weights. 

Manganese Carboiiate, MnCOg, occurs in nature as rhodo- 
chroisite. 

Ferrous Carbonate, FeCOg, occurs in nature as siderite. 
The basic carbonates of iron are often seen as '* iron stains." 
The ferrous dicarbonate is held in solution in chalybeate 
waters. As soon as the excess of carbon dioxide is removed, 
the iron is deposited as a shmy mud, consisting of basic fer- 
rous carbonate, which absorbs oxygen, becoming reddish 
brown with the formation of ferric compounds. 

Bismuth forms several basic carbonates; one, for exam- 
ple, has the formula (BiO)2C03. 

Sulphides of Carbon 

Several sulphides of carbon probably exist, but the impor- 
tant one is carbon disulphide, CS2, which is formed by the 
direct union of the elements, sulphur vapor being led over 
heated carbon : — C + 2 S = CS2 — 19,600 cal. This is done 
now in an electric furnace (process of Taylor). When pure, 
it is a colorless, rather pleasant smelling liquid ; sp. gr. 1.29. 
On standing, however, it becomes somewhat colored and 
usually has a very disagreeable odor. It evaporates very 
readily and absorbs heat. While it has a b.-p. of + 47°, 
it remains a liquid down to —116°. It refracts light 



CARBONATES OF THE REMAINING GROUPS 25 1 

strongly. It is very insoluble in water, but mixes with 
alcohol and ether in all proportions. It is a good solvent 
for oils, fats, sulphur, phosphorus, and iodine. It burns 
with a blue flame : — 

CS2 + 3 02 = C02 + 2S02. 

Corresponding to H2CO3, we should expect H2CS3, TJiio- 
carboiiic Acid, which may be looked upon as a result of the 
union of H2S and CS2. It is very unstable, but forms a 
series of stable salts. The best known one of these is cal- 
cium thiocarbonate, CaCSg. 

Salts of Ortho-TJuocarbonic Acid, C(SH)4, or H^CS^, are 
known. 

COS, Carbon Oxy-sidphide^ is also known. 

EXERCISES 

1. How do the principles of vapor tension apply to calcium 
carbonate when it is heated in a closed tube ? 

2. What is the percentage of (^) barium oxide in witherite ; 
{p) strontium oxide in strontianite ; {c) zinc oxide in calamine? 

3. Complete the reaction 

X Al2(S04)34-J' NasCOg + w H.O = 

4. How much white lead should be obtained theoretically from 
65 kilograms of lead ? 



CHAPTER XXXIX 
SILICON OXIDES, SILICATES, GLASS, EARTHENWARE 

Silicon Dioxide, silica, SiOa, is the only solid oxide of 
silicon occurring in nature. Silicon Monoxide, '' monox," 
SiO, is prepared by heating the dioxide mixed with carbon 
in a vacuum electric furnace (Potter). The oxides of car- 
bon formed are removed from the sphere of reaction by 
the reduced pressure. It is a yellow-buff powder in such 
a fine state of subdivision that it remains suspended in 
water through a long period of time. 

The natural siHcon dioxide is one of the extremely 
important constituents of the earth's surface. It occurs 
as rock-crystal (hexagonal system), quartz, flint, agate, 
tridymite, and, in variable sized grains, as sand. It forms 
several of the precious stones, as amethyst, bloodstone, 
chalcedony, moss agate, and smoky quartz. It is one of 
the mineral constituents of many rocks, as granite and 
syenite. It has a specific gravity of 2,7. 

Silicon dioxide may be prepared by heating the hydrox- 
ides, which are obtained by precipitation. This form is an 
amorphous powder with a specific gravity of 2.2, and is 
so fine that it may be poured from one vessel into another 
in a stream like a liquid. 

Silica melts transiently at + 1800°, when it may be spun 
into wool or made into various shapes. When heated 
higher, it becomes a clear liquid, which on cooling crystal- 
lizes and is transparent like glass. In fact, it is more 
transparent than glass to light of certain wave lengths. 

252 



SILICON OXIDES, SILICATES, GI.ASS, EARTHENWARE 253 

The invisible rays as short as 250 ixfi pass through quartz 
vessels. Fused quartz is very hard and brittle, but pos- 
sesses a small coefficient of expansion. A quartz vessel 
heated red hot may be plunged into cold water without 
being broken. Glass with similar treatment is shattered. 

Silicon dioxide is insoluble in water and in all acids, 
except hydrofluoric acid : — 

Si02 + 4 HF :^ >^ SiF^ + 2 H2O. 

It forms a soluble compound, a siHcate, with the alkaline 
oxides, especially when heated : — 

SiO^ + 2 Na.p = Na^SiO^. 

Silicon Hydroxide, silicic acid, orthosilicic acid, Si(OH)4, 
is prepared by precipitating an aqueous solution of the 
alkaline silicates by means of a mineral acid : — 

K^SiO^ + 4 HCl = 4 KCl + >k H^SiO^. 

All of the silicic acid does not separate as a gelatinous 
precipitate (hydrogel), some remaining in solution in water 
(hydrosol). The former is an almost colorless, gelatinous 
mass, which can be dried to a white powder. It easily loses 
part of the water, forming SiO(OH)2, or metasilicic acid, 
and on further heating, silica (SiOg). The silicic acids are 
insoluble in acids, but are soluble in alkalies. 

The salts of these acids are known as silicates. The 
soluble silicates, K4Si04 or K2Si03, and Na^SiO^ or 
NagSiOg, are formed by fusing quartz or sand with the 
alkaline hydroxides. These are known as "water glass" 
and are soluble in water. They are used in surgical dress- 
ings, the manufacture of refractory cements, and in making 
glass. 

Glass may be defined as an amorphous, transparent or 
translucent mixture of silicates, one of which is usually that 



254 GENERAL INORGANIC CHEMISTRY 

of an alkali, with the general formula M^20, N"0, 6 5102- 
M^ may be sodium or potassium, when the glass is known 
as a " soda " or " potash " glass ; and N^^ may be calcium 
or lead, when the material is known as a ** lime " or " lead " 
glass. A " soda-lime " glass would have the generic for- 
mula NagO, CaO, 6 Si02. Glass is made by melting various 
substances, which, . during the heating, yield the oxides 
referred to, in an open or covered pot constructed of clay, 
or in a special furnace. Often borates or phosphates are 
added to make the material melt at a lower temperature. 
Glass does not melt at a definite temperature, but, when 
heated, first softens and remains plastic through many 
degrees before becoming a limpid liquid. This conduct 
allows its working during the plastic stage by blowing, 
flattening, molding, and so forth. The constituents of 
which glass is made nearly always contain impurities, as 
the oxides of iron or other metals, which give the product 
color. In fact, many oxides or free metals are added to the 
"batch " to give glass a characteristic color. When color- 
less glass is wanted, the color effects produced by such 
impurities as iron are overcome by ** bleaching." This 
is accomplished by adding manganese oxides in such pro- 
portions that the pink color produced by these oxides 
complements that resulting from the presence of the iron 
compounds and the glass appears colorless. Glass is 
known technically by other names than those which give 
an indication of its chemical composition ; for instance, 
blown, window, crown, plate, cut, and so forth. These 
terms are associated with the devices used in producing a 
particular form, or the subsequent mechanical treatment 
to secure a particular finish. Glass is a mixture of silicates, 
some of which, if allowed to cool very slowly, solidify as 
crystals, and thus the glass is *' devitrified." If glass is 



SILICON OXIDES, SILICATES, GLASS, EARTHENWARE 255 

cooled too quickly, the exterior is hard but the glass is very 
brittle. It is aimed to cool the glass quick enough to avoid 
devitrification and at the same time to make it as tough as 
possible. As one of the silicates is that of an alkali, glass 
is always more or less soluble in water. 

Other Silicates. A large portion of the earth's surface 
is made up of silicates, limestone being the chief additional 
formation. The siHcic acids are quite unstable and are 
readily separated from their soluble salts by weak mineral 
acids. With these exceptions, the silicates are very stable. 
Many siHcates are soluble in hydrochloric acid, and often 
during the solution one of the silicic acids separates out. 
All the silicates are acted upon more or less by hydrofluoric 
acid. Many are decomposed, however, only by fusion with 
the alkaline hydroxides or carbonates, which produce the 
silicates soluble in water or mineral acids. 

A study of the silicates is one of great interest and im- 
portance to the mineralogist, geologist, and agronomist. 
This brings to our notice the fourth desirable thing to know 
of compounds ; namely, the relation of the atoms in the 
molecules. Confessedly, we do not actually know this 
relationship, nor are we able to depict it on a flat surface, 
but for the sake of convenience we make use of graphic 
formulas, which are most helpful in securing a better 
understanding of the constitution of many compounds, 
which otherwise appear quite complicated. 

If we start with orthosilicic acid, one or more molecules, 
and remove water, molecule by molecule, we secure types 
like the following : — 

sCoH-H20 = Si=0 ; 

Orthosilicic acid. Metasilicic acid. 



256 



GENERAL INORGANIC 


CHEMISTRY 


/OH-H2O 

^'>OH 
\0H 




Si-OH 


-H2O 
/OH 

\0H - H2O . 




>0 ; and 
Si-OH 
^0 

H^SiA-- 


Si-OH 


Si(0H)4-H,0 
Si(OH),:gO 


■ = si<;oH- 


Si(0H)4- H2O. 




Si^OH 

^0 



Trisilicic acid (H^SigOg). 

The last less H2O gives H2Si307 ; then H2Si409, and 
so on, are obtainable. Several well known minerals are 
built up on these types. 



^O 



Si 



/^?*~ 



to 
o 



Mg 



/OK 

s<o\ 
^o7 



Al 



/O 

Si^OK 

^O 

Si^O 

/9 



Al; 



Si 



= 
\0- 



Ca 



\0 



Si = 0. 



MgsSiO^. 
Olivine. 



KAlSiO^. 
Mica. 



KAlSi308 
Feldspar. 



CaSiOg. 

Wollastonite. 



Rocks are made up of mixtures; granite, for example, is 
composed of silica, mica, and feldspar. The soil is com- 



SILICON OXIDES, SILICATES, GLASS, EARTHENWARE '25/ 

posed of mixtures of these silicates and others produced 
by their disintegration through chemical and physical 
influences. For example, feldspar is decomposed by long 
contact with water charged with carbon dioxide : — 

2 KAlSi308 + C02 + 2 H20 = 4 Si02+ H4Al2Si209 + K2C03. 

The potassium carbonate is leached out by more water 
and thus becomes available as plant food. The hydrated 
aluminum silicate, Al2Si207, 2 H2O, which may be written 
AI2O3, 2 Si02, 2 H2O, is known as kaoHnite, or '* primary," 
or "lean" clay, and has a granular structure somewhat 
similar to that of the original feldspar. When through 
mechanical influences it is pulverized, transported in sus- 
pension by water, and subsequently deposited, the particles 
become covered with a very thin coating of silicic acid, and 
the clay acquires new properties, such as plasticity. It is 
then known as kaolin, "secondary," or "fat" clay. The 
property of plasticity increases on standing in a damp 
condition, so clays are often "ripened" by keeping them 
wet for a number of months. Clay acquires a characteristic 
odor when breathed upon. When it is heated, water is 
lost, the material shrinks, and a hard, difficultly fusible 
porous mass remains. We are familiar with it in earthen- 
ware and bricks. To reduce the shrinkage to a mini- 
mum the clay is frequently mixed before shaping with 
pulverized feldspar and previously burned clay. The colors 
of earthenware are due to the impurities present, mainly 
compounds of iron. When the temperature is sufficiently 
high, the material fuses. Usually, however, clay is used as 
a basis for shaped vessels which are then baked; "biscuit 
firing" it is called. The rigid porous mass thus prepared 
is then dipped into a milk made of mixed fusible siUcates 
suspended in water. On heating again, the silicates. 



258 GENERAL INORGANIC CHEMISTRY 

fuse and form an impervious coating or glass on the 
exterior ; the resulting product is known as porcelain. 

The term ''clay," which means a substance of fairly 
definite composition to the chemist, is applied by the 
agronomist to rock of variable composition, but of such a 
state of subdivision that it is readily transported in sus- 
pension in water. Silt, which is composed of particles 
next greater in size mixed with clay, constitutes the basis 
of "alluvial soils." 

EXERCISES 

1. Calculate the percentage of silica in mica^ 

2. Suppose a glass had the formula NaaO, CaO, 6 Si02, how 
much sodium carbonate and hmestone would be necessary to 
make 250 pounds? 

3. Write graphically the formula for dehydrated aluminum 
silicate. 



CHAPTER XL 
THE REMAINING OXIDES AND SULPHIDES OF GROUP IV 

The Positive Series 

TiO CeO 

Ti(OH)2 Ce(0)H2 



TigOg CcgOg 

Tibg Zr02 CeOg ThOg 

Ti(6H)4 Zv(6u\ Ce(OH)4 Th(0H)4 

TiO(OH)2 ZrO(OH)2 



Zr^Og • Th^Og 

Titaiiiimi Dioxide, Ti02, may be prepared as a white 
powder, but it occurs in nature as rutile. It is widely 
distributed and is often found in iron ores. Its presence 
in iron ores has been regarded as very objectionable. How- 
ever, with the modern methods of electric smelting of iron 
ores, it has proved to be less troublesome. The salts of 
metatitanic acid, H2Ti03, are important ores of titanium, 
as menaccanite, FeTiOg, and perovskite, CaTiOg. Poly- 
metatitanic acid has the formula HjQTigOjg. 

Zirconium Dioxide, zirconia, Zr02, is found in nature as 
the precious stone hyacinth or jacinth. When prepared 
it is a white, difficultly fusible body which is used in the 
Linnemann and Nernst lights, and in incandescent gas 
mantles. 

TJiorium Dioxide, thoria, Th02, is the basis of the Wels- 
bach incandescent gas mantle. Ceriimi Oxide, ceria, is 
usually present to the extent of one or two per cent. The 

259 



26o GENERAL INORGANIC CHEMISTRY 

mantle is made by saturating a fiber stocking with the 
mixed nitrates. After drying, the cotton is burned away. 
A network of the oxides remains behind, constituting the 
mantle, which is suspended above a Bunsen gas burner. 
The character of the light produced varies with the per- 
centage of ceria present. The exact role played by the 
ceria has not been definitely explained. Its efficiency is 
probably due to the fact that the oxides of cerium are 
readily convertible one into the other. The gas mixture 
doubtless reduces and oxidizes the ceria, which changes 
facilitate the combustion of the gas by increasing the tem- 
perature. 

The Szilphides of this series are made by fusion and are 
decomposed by water. 

Negative Series 



GeO 

Ge(OH)2 



GeOg 



GeS 
GeSr 





Pb20 


SnO 


PbO 


Sn{0H)2 [Sn20(OH)2] 


Pb(OH), 




Pb^Os 




-?\o. 


SnO^ 


Pb02 


SnO(OH)2 (HioSn.Ois) 


PbO(OH> 


SnS 


PbS 


SnSo 





Stamious Oxide, SnO, is made by heating stannous 
oxalate (SnC204) without the presence of air. It blackens 
on exposure to sunlight, absorbs oxygen, and is pyrophoric. 
The stannous salts, as SnCl2, are derived from it. 

Stannic Oxide, Sn02, occurs in nature as tinstone or 
cassiterite, in quadratic crystals or in a compact brown 
mass with a specific gravity of 6.J. It is the sole source 
of tin. The artificial oxide is white, and is prepared by 



REMAINING OXIDES AND SULPHIDES OF GROUP IV 261 

burning the metal in the air or by treating it with nitric 
acid and subsequently heating the product. Metastannic 
acid, SnO(OH)2, and poly-metastannic acid, Hi^Sn^Oi^, 
form soluble salts with the alkaline hydroxides. NagSnOg, 
3 H2O is used as a ''preparing salt" in calico printing. 

The tin sulphides are formed by the precipitation of 
the corresponding salts with H2S. Stannic Sulphide, 
SnS2, is a yellow substance, which dissolves in alkaline 
sulphide solutions to form thio-salts : — 

SnS2 + Na2S = Na2SnS3, 

sodium thio-metastannate. When treated with an acid, 
the H2SnS3, which, one would expect, decomposes into 
SnS2 and 1^2-^' ^^^ latter being evolved. Stannous Sul- 
phide, SnS, is brown and insoluble in ammonium sulphide, 
(NH4)2S, but is soluble in the disulphide, (NH4)2S2, the 
extra sulphur changing the tin from the stannous to stannic 
form (oxidation by sulphur) : — 

SnS + (NH4)2S2 = (NH4)2SnS3. 

Lead Monoxide, htharge, massicot, PbO, is formed by 
heating lead in the air. It is a heavy, yellow-buff or red- 
dish powder, stable when heated alone, but easily reduced 
by carbon or by hydrogen, and insoluble in water. It is 
used in the manufacture of red lead, glass, and the salts of 
lead, as the nitrate, acetate, and carbonate. 

Red Lead, minium, PbgO^, is prepared by carefully heating 
the monoxide in the air. It is a brilliant red, crystalline pow- 
der, with specific gravity of ^.6 to 9.1. It forms no hydrox- 
ide, is decomposed by acids, and appears to be composed 
of the monoxide and dioxide, 2 PbO, Pb02, or PbgPbO^. 

Lead Dioxide, Pb02, occurs naturally in small quantities 
as plattnerite. It is made artificially by treating red lead 
with nitric acid or chlorine. The brown powder is decom- 



262 GENERAL INORGANIC CHEMISTRY 

posed on heating into PbO and O, hence it has strong 
oxidizing power. The hydroxide, PbO(OH)2, is known as 
metaplumbic acid. 

The other lead oxides are thought to exist ; namely, lead 
suboxide, PbgO, a black powder, easily decomposed by 
heat; and lead sesquioxide, Pb203, which may be con- 
sidered a compound of the monoxide and the dioxide, 
PbO,Pb02, o^ t^^ ^^^^ ^^^^ ^f metaplumbic acid, PbPb03. 
It is a yellow powder which forms no class of compounds. 

Lead Stilphide, PbS, occurs naturally as galena and is 
the chief ore of lead. 

EXERCISES 

1. If monazite sand contains 4 per cent of Th02, how many 
tons of the sand would be necessary to produce twenty-four 
million mantles, if each mantle weighed 6 grams? 

2. How much red lead could be made from 800 kilograms of 
litharge ? 

3. Complete the reaction : — 

X PbOs ^y HCl = z PbCl, -f w HsO-f 



CHAPTER XLI 



Group V 



NITROGEN OXIDES AND THEIR DERIVATIVES 

The oxides of nitrogen possess unique properties. They 
and their derivatives play such a prominent part in nature 
that their consideration involves some of the most important 
phenomena of both practical and theoretical interest. The 
comparable properties of the five oxides are set forth in 
the table. They present a splendid illustration of the law 
of multiple proportions. 





Monoxide, 


Dioxide, 


Tkioxide 


Tetroxide, 


Pentoxide 


Nitrogen 


Nitrous LIxide 

" Laughing 

Gas " 


Nitric 
Oxide 




Peroxide 




P^ormula 


N2O 


NoO. * 
(NO) 


N-Os 


N2O4 
(NO2) 


N205 


Physical state .... 


gas 


gas 


gas 


liquid 


solid 


Appearance 


colorless 


colorless 


brown-red 


colorless 


white 


Boiling point .... 


- 89.8° 


-142° 


-3.5° 


26° 


+ 45° 


Melting point .... 


- 102.3° 


- 150° 


-21° 


-11° 


+ 30° 


Specific gravity . . . 


1-53 


1.039 


145 
(blue) 


1.49 
(red gas) 




Spec. grav. liquid . 


0-937 






1.50 




Corresponding acid 


hyponitrous 


none 


nitrous 


none 


nitric 


Formula 


HNO 




HNO2 




HNO3 


The sulphides are . 






N.2S3 


N2S4 


N2S5 



* NO is the actual formula. N2O2 is given to emphasize the law of multiple 
proportions. 

261, 



264 GENERAL INORGANIC CHEMISTRY 

Nitrogen Monoxide, nitrous oxide, *' laughing gas," N2O, 
is prepared by heating ammonium nitrate : — 

NH4N03 = |N,0 + 2H20. 

It is a colorless gas with a pleasant smell and sweet 
taste, and is somewhat soluble in water and alcohol. It 
may be collected over warm water, in which it is only 
slightly soluble. It supports combustion, if the combustion 
has been actively started. A strongly burning taper is not 
extinguished by the gas ; phosphorus burns brilliantly, 
whereas slowly burning sulphur does not burn in it. Davy 
learned that it could be breathed, and that it produced 
insensibility if inhaled long enough ; therefore, it is used 
alone as an anesthetic in minor surgical operations, and 
followed by ether or chloroform in major operations. It 
does not combine directly with water to form an hydroxide. 

Hyponitrons Acid, HNO, would appear to be the result 
of the following reaction: N2O + H^O = 2 HNO. The 
compound is prepared indirectly, however. A hyponitrite is 
first produced by reducing a nitrite with sodium amalgam, 
and the hyponitrite is then decomposed by means of an 
acid. It is a very weak, unstable acid, and from its re- 
actions cannot really be considered an hydroxide of nitrous 
oxide. 

Nitrogen Dioxide, nitric oxide, N2O2, or NO, is prepared 
by the action of certain metals, as copper, upon nitric 
acid : — 

3 Cu + 8 HNO3 = f 2 NO + 3 Cu(N03)2 + 4 H2O. 

On coming in contact with oxygen or the air, brown-red 
fumes of the higher oxides are formed at once. It sup- 
ports combustion, but less readily than nitrous oxide. 
Burning sulphur will be extinguished in it, but phosphorus 



NITROGEN OXIDES AND THEIR DERIVATIVES 265 

will continue to burn. Mixed with carbon disulphide it 
burns with a brilliant light with high actinic properties. 
It is dissociated at elevated temperatures. It is neutral in 
reaction and forms no hydroxide or acid with water, in 
which it is insoluble. It is readily soluble in a solution of 
ferrous sulphate, which it colors brown. It is poisonous 
when breathed. 

A^iirogcii Trioxidc, N2O3, is formed by the action of 
starch, sugar, arsenious oxide, or other easily oxidizable 
substances, upon nitric acid : — 

AS2O3 4- 2 HNO3 + 2 H2O - \ N2O3 + 2 H3ASO4. 

The blue liquid at low temperatures changes to a brown- 
red gas when heated. At ordinary temperatures it ap- 
pears to be a mixture of NO and NO2. It dissolves in 
ice-cold water, producing a blue liquid, which is Nitrons 

N203+H20 = 2HN02. 

It is a very unstable acid and is known only in solution. 
It is easily decomposed into nitric acid and nitric oxide. 
The salts, nitrites, are fairly stable. They may be pro- 
duced by the reduction of nitrates, sometimes by simply 
heating, or by the oxidation of ammonia. The nitrites occur 
naturally in the atmosphere, in rain and soil waters, and 
in plant and animal juices, but in very small amounts. 
When thrown upon hot charcoal, they deflagrate. Sodium 
nitrite is extensively used in making organic compounds. 
The nitrites are decomposed by stronger acids : — 

2 KNO2 + H2SO4 = K2SO4 + 2 HNO2, 

and 3 HN02= HNO3+ N2O2 +H2O. 

Nitrogen Tetroxide^ nitrogen peroxide, N2O4, or NOg, is 



266 GENERAL INORGANIC CHEMISTRY 

formed when nitric oxide is brought in contact with the 
proper amount of oxygen : — 

N2O2 + 02= N2O4. 

It is also formed by the decomposition of some of the 
nitrates by heat : — 

Pb(N03)2 = N2O4 -h PbO + O. 

N2O4 is a colorless liquid at low temperatures, solidify- 
ing at — 20° C. On slight rise of temperature it is dis- 
sociated wholly into NO2, which is a red-brown gas at 
+ 140°. It forms no distinctive hydroxide of its own, but 
on solution in water, nitrous and nitric acids are formed : — 

2 NO2 + H2O = HNO2 + HNO3. 

It is a powerful oxidizing agent, but does not readily 
support combustion, although phosphorus can be made 
to burn in it. It is very poisonous when breathed. 

Nitrogen trioxide and nitrogen tetroxide readily lose 
oxygen, changing into the dioxide, when brought in con- 
tact with a reducing substance, as sulphur dioxide. This 
is observed by the gases becoming colorless. When more 
oxygen is brought in contact with the nitrogen dioxide, 
the other oxides are re-formed and again exercise their 
oxidizing action. This property of causing free oxygen 
to combine with substances not so affected under normal 
conditions is taken advantage of in the manufacture of the 
most important of all chemicals, sulphuric acid. 

Nitrogen Pentoxide, N2O5, is prepared by removing water 
from nitric acid by means of a powerful desiccating agent, 
as phosphorus pentoxide : — 

2HNO3-H2O + N2O5. 



NITROGEN OXIDES AND THEIR DERIVATIVES 267 

It is also prepared by the action of chlorine upon silver 
nitrate : — 

2 AgNOg + CI2 = 2 AgCl + Np, + O. 

Nitrogen pentoxide decomposes spontaneously. It com- 
bines with water with great energy to form nitric acid, 
which will be considered in the next chapter : — 

N,0, + H,0 = 2HNO,. 



EXERCISES 

1. How much air would be necessary to change 6 liters of 
nitrogen dioxide into the trioxide? (Consider all measurements 
at 0° and 760 mm.) 

2. How much nitrogen tetroxide may be made according to 
theory from 8 g. of lead nitrate ? 

3. What volume of "laughing gas," measured at + 20° and 
750 mm., may be made from 12 g. of ammonium nitrate? 



CHAPTER XLII 

NITRIC ACID AND THE NITRATES 

Nitric Acid, '' aqua fortis," HNOg, was one of the earliest 
known acids. It is formed in the process of decay of 
nitrogenous organic matter in the presence of an excess of 
oxygen and strong bases, by which it is at once neutraHzed. 
In this way we can account for the large deposits of 
nitrates found in various parts of the world, as the potas- 
sium nitrate (Bengal saltpeter) of India and Persia, and the 
sodium nitrate (Chili saltpeter) of Chili and Peru. It can 
be formed by the action of an electric spark upon moist 
air. It is therefore found in the air as a nitrate after 
electric storms and in rain water. Several modern methods 
for preparing this important acid depend upon duplicating 
natural processes in efforts to utilize the abundance of 
nitrogen in the atmosphere. For example, the air is 
sparked by high-tension currents, and the products resulting 
are quickly removed to a colder place, as they are readily 
decomposed at the elevated temperature. Nitric acid is 
usually prepared, however, by treating a nitrate with a 
stronger non-volatile acid, as sulphuric acid : — 

2 NaN03 + HsSO^^ Na2S04 -f 2 HNO3. 

The heating must be gentle, as the acid is decomposed 
at high temperatures. It is concentrated and purified by 
redistillation with sulphuric acid and passing air through it 
in the dark, since it is decomposed by bright light. 

Nitric acid is ordinarily a colorless liquid, b.-p. + '^^'^^ 

268 



NITRIC ACID AND THE NITRATES 269 

which becomes a soUd at — 47°. The specific gravity of 99.8 
per cent acid is 1.56. It fumes in the air and turns yellow 
in the light and on heating. This is due to partial decom- 
position, the oxides of nitrogen separating and dissolving in 
the acid. The effect of heat is to decompose it, as follows : 
2 HNO3 = 2 NO2 + H2O -f O. The ordinary concentrated 
acid contains 68 per cent acid, and has a sp. gr. of 1.42 and 
distills at + 123°. When the concentrated acid has dis- 
solved nitrogen tetroxide until it has a specific gravity of 
about 1.5, it acquires a deep red color and is known as 
fuming nitric acid. 

Nitric acid is extensively used in the separation of gold 
and silver, and in the manufacture of explosives, coal tar 
dyes, and synthetic medicinal preparations. It is a power- 
ful corrosive poison. It colors the skin yellow and attacks 
organic matter vigorously. It is a strong oxidizing agent. 

Actiofi of Nitric Acid. — Usually when a metal is dissolved 
in an acid, hydrogen is evolved ; with nitric acid, however, 
if any hydrogen is liberated, it reacts with more nitric acid. 
The reaction may be looked upon as taking place in two 
stages. If a strong acid is used, the reactions may be 
written so : — 

3 Zn + 6 HNO3 r>: 3 ZKNOe)^ + f 3 H^, 
and 3 H.2 -f- 2 HNO3 = 4 H2O + t2 NO, 
or 3 Zn + 8 HNO3 -^ 3 Zn(N03).2 + 4 H2O + f 2 NO. 

If we use a very weak acid (5-6 per cent), the reaction 
takes place in this way : — 

Zn + 2 HNOgZ^ Zn(N03).2 + \ H2, 
2 HNO3 H- 4 H. = NH4NO3 + 3 H2O. 
With some oxides the reaction is as follows : — 
ZnO + 2 HNO3 -^ Zn(N03)2 + H2O. 



270 GENERAL INORGANIC CHEMISTRY 

With some elements, as, for example, tin and antimony, 
the acid exerts a powerful oxidizing action. The nitrates 
are not formed, nor are the metals brought in solution, but 
the oxides or hydroxides are produced. These are not 
soluble in nitric acid. White insoluble compounds are 
produced. 

Aqita Regia is the name given to a mixture of concen- 
trated hydrochloric and nitric acids, usually in the propor- 
tion of 3:1. Gold and platinum do not dissolve under 
ordinary conditions in either of these acids singly, but they 
dissolve readily in aqua regia. Its powerful solvent action 
is attributed to the formation of chlorine and nitrosyl 
chloride : — 

3 HCH- HNO3 = 2 H2O + NOCl + CI2. 
The Nitrates 

Nitric acid is a monobasic acid and its compounds are 
called nitrates. Here we have hydrogen joined to an 
electro-negative radical. The nitrates are numerous and 
very important. They are usually crystalline soUds, solu- 
ble in water, losing oxygen on being heated, and decom- 
posing energetically when heated with oxidizable matter. 
They melt easily, and when heated on charcoal they defla- 
grate. Some nitrates of the less positive elements, as 
bismuth, are decomposed by water, forming basic nitrates 
similar to the basic chlorides. 

Sodmm Nitrate, cubic niter. Chili saltpeter, NaNOg, is 
had in an impure form from Peru, Bolivia, and Dakota, 
called "caliche." Large quantities are used annually in 
the manufacture of sulphuric acid, also in the manufacture 
of inferior gunpowder, and in fertilizers. The commercial 
form usually carries about 98 per cent NaNOg. It attracts 
moisture. 



NITRIC ACID AND THE NITRATES 27 1 

Potassium Nitrate, niter, saltpeter, Bengal saltpeter, 
KNO3, is found in India, Persia, Egypt, and in the filthy 
parts of certain cities. It is formed by the decay of nitrog- 
enous matter in rainless seasons and in sheltered places, 
when an alkaline base is present. These conditions are 
artificially produced in what are known as " niter-planta- 
tions." Nitrogenous organic matter, porous earth, wood 
ashes, and so forth, are heaped up and allowed to stand 
for many months. The mass is then leached and the solu- 
tion evaporated until the niter crystallizes on cooling the 
concentrated liquor. The changes are the result of the 
action of the Bacillus nitrificans. Potassium nitrate is now 
largely made also by double decomposition : — 

KCl + NaN03 = KNO3 + NaCl. 

This action is dependent upon the difference in solubility 
at different temperatures of the salts present. Potassium 
nitrate is not hygroscopic. It is used in the manufacture 
of the finer grades of gunpowder and other explosives, for 
making matches and fireworks, and for curing meat. 

Gunpowder. — The knowledge of the propelling force of 
gunpowder-like mixtures came about between 13 13 and 
1325 A.D., and Berthold Schwarz, a Benedictine monk, 
invented the guns for utilizing this force (Guttmann). 
Gunpowder consists of an intimate mixture of saltpeter, 75 
per cent, charcoal, 12 to 15 per cent, and sulphur, 13 
to 10 per cent; its composition varies according to the 
purpose for which it is to be used. The finely pulverized 
materials are thoroughly ground together in a moist con- 
dition and then pressed into sheets, which are broken and 
dried. The moist mass may be pressed into molds of 
various sizes and shapes before drying. The force exerted 
in the explosion is due to the sudden production of a large 



2/2 GENERAL INORGANIC CHEMISTRY 

amount of gas, which is greatly expanded by the high 
temperature generated in the combustion. The principal 
gases are carbon dioxide, carbon monoxide, nitrogen, and 
water ; and the chief solid products are potassium carbon- 
ate, sulphide and sulphate, and free sulphur. 

Silvei' Nitrate, lapis infernalis, lunar caustic, AgNOg, is 
the chief salt of silver. It is made by solution of the 
metal in nitric acid, and subsequent evaporation to crystal- 
lization : — 

3 Ag + 4 HNO3 ^ 3 AgNOg + 2 H^O -h | NO. 

It fuses at + 225° and may be cast in small sticks. It 
cauterizes organic matter and is poisonous. It is easily 
decomposed by contact with organic matter, as dust, 
paper, and the skin. It is the foundation of some indelible 
inks. 

Calcium Nitrate, Ca(N03)2, is sometimes found in nature 
in small amounts, as a result of similar changes noted in the 
formation of the alkaline nitrates. The anhydrous salt is 
used in the laboratory for drying nitrogen peroxide. 

Strontium and Barium Nitrates, Sr(N03)2 and Ba(N03)2, 
are used in fireworks to produce red and green fires, re- 
spectively. 

Lead Nitrate, Pb(N03)2, ^^ ^^^^ ^'^ dyeing and calico 
printing, in the making of chrome-yellow, and in photog- 
raphy. 

Ferric Nitrate, Fe(N03)3, is used in dyeing silk black 
and cotton buff. 

Basic Niti'ates are formed by mercury, bismuth, iron, 
and some other metals. 

Bismuth Subnitrate, bismuth oxynitrate, bismuthyl ni- 
trate, BiONOg, is used as a cosmetic, and in medicine. 



NITRIC ACID AND THE NITRATES 273 

EXERCISES 

1. Write the reactions of hydrochloric and nitric acids upon 
zinc, one beneath the other, and compare the formulas. 

2. Sodium and potassium chlorides and nitrates are soluble in 
water. Why then should potassium nitrate instead of sodium ni- 
trate be obtained when a mixture of the salts in a water solution 
is evaporated ? 

3. What is the percentage of nitrogen in "caliche" that is 
97.8 per cent pure? 

4. How much sodium nitrate (98. per cent pure) would have 
to be present in a fertilizer that contained 4 per cent of nitrogen, 
assuming that all the nitrogen came from the nitrate ? 



CHAPTER XLIII 

OXIDES AND SULPHIDES OF THE OTHER ELEMENTS OF 

GROUP V 

A TABLE showing the composition of the oxides and sul- 
phides brings out the striking resemblances of the ele- 
ments in this group : — 

P,03 P^O, P,0, 

ASgOg AS2O5 

Sb203 SbaO^ Sb^Og 
Bi203 Bi2b4 Biabg 

AS2S3 -AS2S5 

Sb^So Sb^S 



P40 


P.O 








BiO 


P4S 


P^S 


AsjSj 






BiS 



2^5 



Bi^S- 



Phosphorus Trioxide, P2O3, or P40g, is formed by the 
slow oxidation of phosphorus at low temperatures or in a 
limited amount of oxygen. In contact with oxygen, it is 
oxidized to P2O5. The colorless needles, which melt at 
+ 24°, have a garlic-like odor. They combine with water 
to ioxui phosphorous acid : — 

P203+3H20 = 2H3P03. 

This acid is also produced by the decomposition of phos- 
phorus trihalide by means of water : — 

PCI3 + 3 H2O = 3 HCl + P(0H)3. 

274 



OXIDES AND SULPHIDES OF OTHER ELEMENTS 275 

It is a solid (m.-p. + 70°) which deliquesces to a thick 
sirup, absorbs oxygen from the air, and is reducing in its 
action. When heated, the following reaction takes place : — 

4H3P03=PH3 + 3H3PO,. 

Although it has three hydrogen atoms, it is a dibasic acid. 
Its salts are c^W^di phosphites. 

Phosphorus Petitoxide, PgO^, is formed when phos- 
phorus is burned at a high temperature or in the presence 
of an excess of oxygen. It is a crystalUne powder which 
volatilizes at + 250° and dissociates at high temperatures. 
It combines with water with a hissing sound and the pro- 
duction of much heat. Its strong attraction for water 
makes it a most valuable desiccating agent. It is used 
especially for drying gases. 

In combining with water three reactions may take place, 
depending upon the proportions present : — 

{a) P2O5 + H2O = 2 HPO3 (metaphosphoric acid) ; 

{U) P2O5 + 2 H2O = H4P2O7 (pyrophosphoric acid) ; 

{c) P2O5 + 3 H2O = 2 H3PO4 (orthophosphoric acid). 

Orthophosphoric Acid, H3PO4, is a crystalline sohd, very 
soluble in water. The other phosphoric acids are usually 
made from it. When heated to + 400°, it loses a molecule 
of water and changes to metaphosphoric acid, which is 
called, commercially, glacial phosphoric acid. This acid 
coagulates albumen, whereas the others do not. When 
the temperature is maintained at + 200° to + 300°, one 
molecule of water is lost from two of orthophosphoric acid, 
and pyrophosphoric acid, H4P2O7-, is obtained. Metaphos- 
phoric acid is monobasic, giving metaphosphates; pyro- 
phosphoric acid is tetrabasic, giving pyrophosphates; and 
orthophosphoric acid is tribasic, giving orthophosphates. 
With the last we have three classes of salts, depending 



276 GENERAL INORGANIC CHEMISTRY 

upon the replacement of one, two, or three hydrogen 
atoms, thus: — 

NagPO^, trisodium phosphate, or normal sodium phos- 
phate; 

Na2HP04, disodium hydrogen phosphate; and 

NaH2P04, sodium dihydrogen phosphate. 

The former of the two acid salts, like Na2HP04, and 
Ca2H2(P04)2, or CaHP04, are neutral in reaction, whereas 
the other acid phosphates, like NaH2P04 and CaH4(P04)2, 
are acid in reaction. 

We may substitute the hydrogen by different bases or 
radicals and obtain double phosphates, as NH4MgP04 and 
NH4N'aHP04, H2O. The latter is commonly called micro- 
cosmic salt, or salt of phosphorus. 

Many of these phosphates occur widely distributed in 
nature, but usually in very small amounts. The alkaline 
phosphates are soluble in water, as are some of the acid 
phosphates, especially the dihydrogen phosphates. The 
monobasic hydrogen phosphates are less soluble, some 
being insoluble. The normal phosphates, as, for example, 
calcium phosphate, are insoluble. The phosphates are 
essential to plant and animal life. They occur in the soil, 
urine, and bones. 

CalciiLwi PhospJiate, tricalcic orthophosphate, Ca3(P04)2, 
is the chief constituent in bones. They nearly always con- 
tain a small amount of magnesium phosphate as well. 
Calcium phosphate is found as phosphorite, apatite, and 
in phosphate rock ; these are called mineral phosphates. 
They constitute the material from which phosphorus and 
its compounds are prepared. On treatment with an acid, 
like sulphuric acid, two phosphates are formed which are 
present in phosphatic fertilizers : — 

Ca3(P04)2 + 2 H2SO4 = 2 CaS04 + CaH4(P04)2, 
or Ca3(P04)2 + H2SO4 = CaS04 + 2 CaHP04. 



OXIDES AND SULPHIDES OF OTHER ELEMENTS 277 

The former is soluble in water and is easily assimilated by 
plants ; while the latter is insoluble in water, and is known 
as "reverted" or "precipitated" phosphate. It is readily 
dissolved by dilute acids and certain salts of ammonium, 
as ammonium citrate. It is supposed to be soluble, there- 
fore, in plant juices and taken up as food by the plants. 
The normal tricalcium phosphate is dissolved only by 
strong acids. 

Iron and Ahiminum Phosphates occur naturally and are 
insoluble in water. 

HypophospJwroiis Acid, H3PO2, is obtained by the decom- 
position of the phosphides of Group II with water, or as 
follows : — 

4 P + 3 NaOH + 3 H2O = 3 NaH2P02 + \ PH3. 

Below zero it is obtained as white leaflets, which melt at 
4- 174° but decompose on heating. It does not alter in 
the air when dry, but when moist easily absorbs oxygen. 
Hypophosphorous acid is monobasic, only one of the hy- 
drogen atoms being replaced by an electro-positive element 
or radical. It is used in medicine and constitutes the basis 
of Horsford's phosphates. 

Phosphorus Sulphides, P^S, P2S, P2S3, P2S5, are used in 
organic chemistry for the production of thio-compounds. 

Arsenic Compounds 

Arsenic Tinoxide, AS2O3, occurs in nature in small quan- 
tities and is known as "bloom." However, it is usually 
prepared by roasting arsenic ore in the air. The white 
powder obtained is known as "white arsenic" or "poison- 
ous flour." This, when melted, forms " arsenic glass." It 
is hard and vitreous with a sp. gr. of 3.69. It gradually 
changes to "arsenic porcelain," becoming opaque and 



2/8 GENERAL INORGANIC CHEMISTRY 

white, with a sp. gr. of 3.78. It has no odor, but a slightly 
sweetish taste. It melts at + 200°, crystallizing in octa- 
hedra on cooling. It sublimes at + 218°. When the 
vapors are quickly cooled, they crystallize in rhombic 
prisms. It is slightly soluble in water and this solution 
acts as if it contained arsenious acid (HgAsOg), being 
weakly acid to litmus. The oxide dissolves in hydrochloric 
acid. It is an irritant poison. As an insecticide it is used 
in mounting skins. Arsenic trioxide is also used in " fin^ 
ing " glass. 

Aj'senites. — The existence of arsenious acid (HgAsOg) is 
hypothetical, but a number of arsenites are known. They 
are very powerful reducing agents and are poisonous. 
The alkaline arsenites are soluble in water. They crystal- 
lize poorly and are deliquescent. Copper arsenite is a 
brilliant green salt, Scheele's green, which is used as a 
pigment and as an insecticide. Paris green, Schweinfurt 
or emerald green, is the double arsenite and acetate of 
copper [Cu3(As03)2, Cu(C2H302)2-] 

Arsenic Pentoxide, AS2O5, does not occur in nature, but 
is prepared by oxidizing the trioxide with nitric acid. 
AsO(OH)3 is produced, which loses water on heating, 
leaving AS2O5. It is a white deliquescent mass, melting 
when heated. On elevation of temperature, it decomposes 
into arsenic trioxide and oxygen. 

Arsenic Acids. — We have an orthoarsenic acid corre- 
sponding to orthophosphoric acid : — 

AS2O5 + 3 H2O = 2 H3ASO4, 

which combines with \ water to form a solid which melts 
at +100°. This heated carefully to +140-150° gives 
pyroarsenic acid (H4AS2O7). When heated to + 200°, 
metarsenic acid is obtained (HAsOg). Orthoarsenic acid 



OXIDES AND SULPHIDES OF OTHER ELEiMEiNTS 279 

is a crystalline solid with a very unpleasant taste, and is 
poisonous. It is a caustic. These acids combine with 
bases and form a series of arsenates similar to the 
phosphates. 

Arsenic Sulphides. — Arsenic forms three sulphides. The 
trisulphide (AS2S3), which occurs in nature as orpiment or 
auri-pigment, is yellow. AS2S5, arsenic pentasulphide, is 
had by precipitation of solutions of arsenates with sul- 
phuretted hydrogen ; this precipitate is also yellow. An- 
other sulphide, AS2S2, the disulphide, occurs in nature and 
is called realgar. It is ruby-red (sp. gr. 3.5). The sul- 
phides of arsenic are soluble in ammonium sulphide and 
form thio-arsenites and arsenates. Solutions of NagAsSg 
and Na3AsS4, when heated with acids, decompose with 
the evolution of hydrogen sulphide and the precipitation 
of the sulphides : — 

2 Na3AsS^+ 6 HCl = 6 NaCl + 3 H2S + AS2S5. 

Antimony Compounds 

Antimony Trioxide^ Sb203, occurs free in nature. It is 
formed by burning antimony in the air. It is a white 
powder insoluble in water. When heated in the air, it 
changes into the tetroxide. It dissolves in a water solution 
of an alkaline hydroxide, giving salts called metanti- 
monites: — 

Sb203 + 2 KOH = H2O + 2 KSb02. 

Antimony trioxide forms two hydroxides, Sb(0H)3, or 
orthoantimonious acid, and Sb20(OH)4, pyroantimonious 
acid. With strong acids, it acts as a base, and there is a 
great tendency to form basic salts. When a carbonate is 
added to a chloride, the following reaction takes place : — 
2 SbClg + 3 Na2C03 + H.2O = 2 SbO,OH + 6 NaCl + 3 CO2. 



280 GENERAL INORGANIC CHEMISTRY 

Antimony Pentoxide, SbgOg, is prepared by oxidizing the 
element or trioxide. It is yellow and very insoluble in 
acids ; it loses oxygen when heated. Three hydroxides 
can be prepared from it : orthoantimonic acid, HgSbO^, 
pyroantimonic acid, H^SbgOj, and metantimonic acid, 
HSbOg. 

Antimony Tetroxide, Sb204. — When the other oxides are 
heated in the air, either the trioxide takes up an atom of 
oxygen or the pentoxide loses an atom with the formation 
of the more stable tetroxide. It forms no hydroxide. 

Antimony Snlphides. — Antimony trisulphide, Sb2S3, and 
antimony pentasulphide, Sb2S5. The former occurs in 
nature as stibnite and is the most abundant compound of 
antimony found in nature. The natural sulphide is black 
and the artificial is red. The hydrosulphides are analogous 
to those of arsenic and tin. 

Bismuth Compounds 

Bismuth Oxides. — Four oxides are known : Bi203, 
Bi205, Bi204, and BiO. 

The monoxide, BiO, is a brownish powder, oxidizing 
very readily. 

Bismuth Trioxide^ Bi203, occurs naturally and may be 
prepared by burning bismuth or heating the hydroxide. 
The hydroxide may be made by adding an alkaline hydrox- 
ide to a solution of a bismuth salt. Bismuth forms salts 
which are readily decomposed by water into basic salts. 
The basic nitrate and basic carbonate, known as sub- 
nitrate and subcarbonate, are white insoluble powders 
which are used medicinally and as cosmetics. 

BismutJi Pentoxide, BigOg, is obtained by heating meta- 
bismuthic acid, HBiOg. This body is formed by passing 
a current of chlorine through a boiling solution of potas- 



OXIDES AND SULPHIDES OF OTHER ELEMENTS 2S1 

sium hydroxide, holding the bismuth trioxide in suspension. 
Bismuth pentoxide is a very unstable body which forms 
one hydroxide. 

■ BismiitJi Sulphides. — Two sulphides are known, bismuth 
monosulphide, BiS, and bismuth trisulphide, Bi2S3. The 
latter is found in nature and the other is prepared by 
precipitation from the solution of a bismuth salt with 
sulphuretted hydrogen. 

Vanadium Trioxide, V2O3, is a black powder ; and 
Vanadium Pentoxide, V2O5, is a brown mass. H3VO4, 
orthovanadic acid, and HVO3, nietavanadic acid, are the 
acids derived from the pentoxide. 

Colnmbium Pentoxide, Cb205, with HgCbO^, orthocolum- 
bic acid, and Tantalum, Pentoxide, TagO^, and orthotantalic 
acid, H3Ta04, show the resemblances among the com- 
pounds of the other elements of the group. 

EXERCISES 

1. Tabulate the hydroxides of phosphorus, arsenic, antimony, 
and bismuth. 

2. What characteristics become more pronounced with the 
increase of atomic weights in the case of the trioxides of phos- 
phorus, arsenic, antimony, and bismuth? 

3. Magnesium ammonium phosphate, when heated, is converted 
into Mg9P207. Calculate the percentage of arsenic in magnesium 
pyroarsenate. 



CHAPTER XLIV 

Group VI 

THE OXIDES AND HYDROXIDES OF SULPHUR 

The type oxide of this group is MO3, but most of its 
members also form MO2. 

Three oxides of sulphur are recognized: sulphur dioxide, 
SO2 ; sulphur trioxide; SO3 ; and sulphur sesquioxide, 
S2O3, about the existence of which there is some doubt. 

Sulphur Dioxide, SO2, occurs in volcanic gases and the 
gas produced in the combustion of coal carrying pyrites 
(Chapter XII). It is obtained by the burning of sulphur 
or pyrites in the air or oxygen : — 

S + O2 = SO2 ; or 2 FeS2 + 1 1 O = Fe203 + f 4 SO2. 

In the laboratory it is usually prepared by the action of 
metals on concentrated sulphuric acid : — 

Hg + 2 H2SO4 = HgSO^ + 2 H2O + \ SO2. 

Sulphur dioxide is a colorless gas with a suffocating odor. 
It has a specific gravity of 2.2 ; hence, one liter weighs 2.86 
grams. It may be liquefied by cooling to — 1 5°, or sub- 
mitting it to a pressure of three atmospheres. The liquid, 
which has a specific gravity of 1.43, boils at — 8°. It 
forms a crystalline solid at — 76°. Sulphur dioxide is quite 
soluble in water, one part of water dissolving 50 volumes. 
It bleaches organic matter. However, this occurs only in 
the presence of water and is often transient. It acts as a 

282 



THE OXIDES AND HYDROXIDES OF SULPHUR 283 

disinfectant and is particularly efficient in destroying 
objectionable insects. 

Sulphurous Acid, H2SO3, is formed by the solution of 
the dioxide in water : — 

SO2 + H2O = H2SO3. -) 

It is known only in solution and is decomposed by light. 
It is a weak dibasic acid, forming two classes of sulphites, 
normal and acid sulphites, as Na2S03 and NaHSOg. 
When the sulphites are treated with a strong acid, sulphu- 
rous acid is liberated, and it readily breaks up into sulphur 
dioxide and water. 

The sulphites of sodium, magnesium, and calcium are 
used in the preparation of wood pulp in making paper. 
They are deliquescent and very soluble bodies. The nor- 
mal sulphites are more easily crystallized and are less 
soluble. Some of the sulphites are used medicinally. 
They are strong reducing agents, and are frequently used 
in photography and in bleaching woolen, silk, and straw 
goods. 

Hyposulphurous Acid, H4S2O4, or H2SO2, is obtained 
when sulphurous acid is treated with finely divided zinc. 
Apparently hydrogen is given off and another portion of 
the acid reduced : — 

Zn -f H2S03 = ZnSOa + H2 ; H2SO3+ H2 = H2SO2+ H2O. 

This acid, which is known only in solution, appears 
to be derived from the unknown oxide SO. The acid 
and its salts, Jiyposulphites, are powerful reducing 
agents. 

Sulphur Trioxide, SO3, is not formed in large quantities 
by the direct burning of sulphur in the air or oxygen. 
The dioxide is the main product. Sulphur dioxide takes 



284 GENERAL INORGANIC CHEMISTRY 

up one more atom of oxygen by passing the mixed gases 
over finely divided platinum (Schroder contact process) : — • 

SO2 + = 503; 

or on treatment of SO2 with nitrogen trioxide : — 

S02+N203=S03+2NO. 

It was earlier prepared by heating ferrous sulphate : — 

2 FeSO^ = Fe203 + SO2 + S^Og ; 

and later by heating fuming sulphuric acid : — 

H2SO4, SO3 = H2SO4 + SO3. 

Sulphur trioxide is a colorless liquid which crystallizes 
when cooled, and dissociates at a red heat. It usually 
contains a small amount of water and forms long white 
needles. It absorbs water with avidity, producing great 
heat. Sulphur trioxide is used to make fuming sulphuric 
acid, which in turn serves to make 100 per cent acid, and 
in *' sulphonating " carbon compounds. These latter may 
be high explosives, coal-tar colors, or synthetic medicinal 
compounds. 

Sidphuric Acid, oil of vitriol, Ii2S04, is probably the 
most important of all chemicals. On account of its exten- 
sive use, immense quantities are made annually ; in fact, 
the commercial progress of a nation may be judged by the 
amount of sulphuric acid made and used. Over two mil- 
lion tons of sulphuric acid were made in the United States 
in 1908, whereas ten years ago it was half that amount. 
It has been found free in a few rivers (Rio Vinagre) and 
in lake waters which come from volcanic regions. 

A little before 1740, Ward, an EngHshman, made sul- 
phuric acid by burning sulphur and niter together, and 



THE OXIDES AND HYDROXIDES OF SULPHUR 285 

condensing the vapors in a glass vessel containing a little 
water. The reactions involved in this process are the 
basis of the method now in use under the name of the 
"lead-chamber process." The reactions are more or less 
complicated, but for our purpose may be simplified as fol- 
lows : — 

Sulphur, or iron pyrites, is burned to produce sulphur 
dioxide : — 

S + 02l±S02; or 2 FeSg + u O l± Fe203 + t 4 SO2. 

This takes place in the sulphur or pyrites burners. If 
the latter, they are built to burn either lump pyrites or the 
powdered ore, which is known as " fines." 

The sulphur dioxide is oxidized to SO3 : — 

SO2 + N2O3 = SO3 + N2O2 ; or 

2 SO2 + N2O4 = 2 SO3 + N2O2. 

This is accomplished by first passing the gases over a 
pot which contains sodium nitrate to which sulphuric acid 
is added. Nitric acid is evolved, which is reduced to the 
lower oxides by the sulphur dioxide. The mixture of 
gases is then passed into large chambers Hned with lead. 
There water in, the form of steam is added : — 

S03 + H20:±H2S04. 

The oxides of nitrogen, which are expensive, are used 
over again ; therefore air is introduced. The oxygen re- 
forms the tri- and tetroxides of nitrogen : — 

2 N2O2 + 031:^2 N2O3; or N2O2 + 02^^N204. 

The nitrogen trioxide combines with more sulphur diox- 
ide, oxygen, and water to form nitrosyl-sulphuric acid, 
iknown as " chamber crystals " : — 

2 SO2 + N2O3 + O2 + H2O = 2 SO2, OH, NO2. 



286 GENERAL INORGANIC CHEMISTRY 

On addition of water these break up, reforming nitrogen 
trioxide, which again oxidizes sulphur dioxide : — 

2 SO2, OH, NO2 + H2O = 2 H2SO4 + f N2O3. 

This gas can be and is used over and over again, although 
there is more or less loss, as a number of other reactions 
take place. In order to save these oxides of nitrogen as 
far as possible, the escaping gases are passed through con- 
centrated sulphuric acid, which absorbs the tri- and tetrox- 
ides. This is done in a Gay-Lussac tower, essentially a 
lead-lined stack about three meters square and ten to 
twenty meters high. This tower is loosely packed with 
coke, quartz, or other acid-resisting material and is so 
arranged that there is a steady flow of concentrated sul- 
phuric acid from the top to the bottom. The brown and 
red oxides are absorbed by the acid and collected in a res- 
ervoir. This acid is called ''niter acid." 

The "niter acid" gives up these oxides when diluted 
and heated. It is therefore pumped, usually by an " acid 
egg,'' to the top of a similar tower, called the Glover tower, 
which is inserted between the pyrites or sulphur burners 
and the first chamber. The acid is diluted at the top of 
the tower and run over the large surface of acid-resisting 
material inside to the bottom of the tower. The hot gases 
from the burners enter the tower at the bottom and heat 
the liquid as it falls. The oxides of nitrogen are swept 
on into the chambers, where they again perform their 
functions. At the same time the acid is concentrated by 
the heat and collects in a reservoir at the bottom, whence 
it is pumped to the top of the Gay-Lussac tower, to be 
used over again to absorb the escaping nitrogen trioxide. 

Sulphuric acid, condensing inside and on the walls of the 
lead chambers, collects at the bottom. It is called '' cham- 



THE OXIDES AND HYDROXIDES OF SULPHUR 287 

ber acid," and contains from 60 to 78 per cent of sulphuric 
acid with a specific gravity of from 1.5 to 1.7 1. " Chamber 
acid " is quite impure, containing lead, iron, arsenic, and 
other metals, and the oxides of nitrogen. It is first puri- 
fied in part by concentrating in cast-iron stills until it has 
a specific gravity of 1.8 and contains about 80 per cent 
H2SO4. This is commercial *' oil of vitriol." It is further 
purified and concentrated by distillation in platinum stills. 
The gaseous impurities are swept away by the water, which 
passes off with some acid ; the solid impurities accumulate in 
the bottom of the still and are drained away ; while the purest 
acid condenses on the sides of the platinum stills, which are 
cooled by water jackets, and runs off into suitable containers. 

Such purified sulphuric acid has a specific gravity of 1.84, 
and contains about 98.5 per cent acid. It is a colorless, oily 
liquid which mixes with water in all proportions. When 
mixed with water, much heat is evolved and there is a con- 
traction in volume. Its great affinity for water causes it to be 
used extensively as a desiccating agent, especially for drying 
gases. It removes water from organic matter, upon which 
fact its powerful corrosive action when brought in contact 
with living matter is dependent in part. It is very poisonous. 

The metals and their oxides are not readily soluble in 
concentrated sulphuric acid, unless it is heated, when there 
is a decomposition of the acid (oxidizing action). The 
cold concentrated acid frequently has little action, due 
in part, no doubt, to the insolubility of the sulphate formed 
in the concentrated acid. However, the diluted acid is a 
good solvent for a number of the metals and oxides : — 

Fe+ H2SO4 .-z^ FeS04+ ^2 ; 

MgO + H2S04z:^MgS04 + H20 ; 

ZnC03+ H2SO4 t:^ ZnS04+ H2O + CO2. 



288 GENERAL INORGANIC CHEMISTRY 

Sulphuric acid is a dibasic acid which, forms a large 
number of important acid, normal, and double salts. These 
will be considered in the. next chapter. There is scarcely 
any substance used for food, clothing, or shelter which is 
not directly or indirectly dependent upon sulphuric acid. 
It is used in immense quantities for making phosphatic 
fertilizers, coal-tar dyes, medicines, galvanizing and tinning 
iron, high explosives, many chemicals, as hydrochloric and 
nitric acids, sulphates, and so forth. 

Finning SnlpJmric Acid, H2S2O7, is prepared by distill- 
ing ferrous sulphate and collecting the sulphur trioxide 
evolved in concentrated sulphuric acid (Nordhausen acid); 
or by the solution of sulphur trioxide as it is produced by 
the contact process in sulphuric acid. When it has a 
specific gravity of 1.93, it contains 45 per cent of SO3. 
It fumes in the air. It is used to dissolve indigo, and 
in the making of certain dyestuffs and of smokeless 
powders. 

PersnlpJmric Acid, H2S20g, and the persulphates, as 
(N 114)25208, are made by the electrolysis of a very cold 
solution. They are strong oxidizing agents. 

TJiiosulpJuiric Acid, H2S2O3, formerly called hyposul- 
phurous acid, may be looked upon as H2SO4, in which an 
atom of oxygen has been replaced by one of sulphur. Only 
the salts, thiosulphates, are known. When treated with 
an acid, they decompose into water, sulphur dioxide, and 
sulphur : — ■ 

Na2S203 + 2 HClr>2 NaCl 4- tS02 + | S + H2O. 

Sodium Thiosnlphate is the most important salt. It is 
prepared by boiling sodium sulphite with sulphur. It has 
a strong reducing action and is much used in photography 
as "hypo-solution," since the silver halides are soluble in 



THE OXIDES AND HYDROXIDES OF SULPHUR 289 

its water solution. The salt is commercially sold under the 
old name of sodium hyposulphite, which is a misnomer. 

The Thionic Acids constitute a series differing in chemi- 
cal composition by an atom of sulphur. They are H2S20g, 
1^2^303, H.^S^Og, and H2S50g. They form salts and are 
called dithionic, trithionic, and so forth, acids. 

• 

EXERCISES 

1. How much sulphuric acid (80 per cent) should be made 
from 5 tons of iron pyrites which carries 44 per cent of sulphur? 

2. Complete the following reactions: {^d) CuCOg + H2SO4 ; 
{b) NaNOa + H,S04 ; {/) H.S2O, + HoO ; {d) Mg + H2SO4 (dil.) ; 
{e) Al + HoSO, ; (/) Zn + H,S04 (cone). 



CHAPTER XLV 
THE SULPHATES. ALUMS 

Many of the sulphates occur naturally in great abun- 
dance. Most of them are soluble in water and crystaUize 
well. The most insoluble ones are those of the positive 
series of Group II, and lead. 

The sulphates are formed : — 

First, by the action of sulphuric acid upon the metals, 
oxides or carbonates : — 

Zn + H2S04::>ZnS04 -\-\ H2, 

CuO + H2S04:r±CuS04 + H2O, 

Na2C03 + H2S04=:^Na2S04 + H2O 4- f CO2 ; 

Second^ by roasting some of the sulphides, as — 

PbS + 2 O2 = PbSO^ ; 
and 

Third, by precipitation, in the case of the insoluble 
ones: — 

BaCl2 + H2S04r>|BaS04 + 2 HCl. 

Sulphates of Group I 

These are generally white, soluble, crystalline bodies. 
Copper sulphate, which contains water, however, is blue. 

Sodium Sulphate, Glauber's salt, or '' sal-mirabile," 
Na2S04,io H2O, occurs widely distributed in nature, 
especially in various mineral waters and alkali lands. 
When made in the Le Blanc soda process, it is called " salt 
cake," and in the manufacture of nitric acid, "niter cake." 

290 



THE SULPHATES. ALUMS 291 

The salt mentioned is stable at temperatures only below 
+ 35°. Above that temperature it melts, separating into 
a saturated solution of an anhydrous sulphate which alone 
melts at +836°; 100 parts of water dissolve 12 parts of 
Glauber's salt at 0°, 354 at + 34°, and 238 at + 100°. 
This is accounted for by the formation of different hy- 
drates. It readily forms supersaturated solutions. It is 
used in medicine, and in the anhydrous form to make low 
grades of glass. 

Potasshtm Sulphate, K2SO4, occurs in the salt beds of 
Stassfurt. It is extensively used as a fertilizer, especially 
in the form of a double sulphate, under the name of 
kainite, which has the formula K2S04,MgS04,MgCl2,H20. 
It is also used in making ordinary alum. 

Potassium Acid Sulphate, KHSO^, and Potassium Di- 
sulphate, K2S2O7, are white deliquescent solids which are 
used as a flux in fusing and decomposing minerals. 

Copper Sulphate, blue stone, blue vitriol, CuSO^, 5 H2O, 
loses water on heating, and becomes first turquoise blue 
(CuSO^, H2O) and then white (CuSO^). On heating 
higher, copper oxide is formed. It is found in small 
amounts in nature. Copper sulphate is soluble in water 
and is poisonous. It is used in electroplating, dyeing, and 
for an insecticide, as ki making Bordeaux mixture, and in 
purifying water for drinking purposes. 

Sulphates of Group II 

Magnesium Sulphate, Epsom salts, MgSO^, 7 H2O, which 
occurs in many natural mineral waters and in the German 
salt deposits, is a white, crystalline, soluble body. It is 
used medicinally as an aperient. 

Calciiim Sulphate, gypsum, alabaster, CaS04,2 H2O, 
also occurs naturally without water, when it is called 



292 GENERAL INORGANIC CHEMISTRY 

anhydrite. When heated to + iio°or -f- 120°, most of the 
water is driven off and plaster of Paris is formed. This is 
capable of reabsorbing water and "setting," or hardening. 
It is therefore used in surgery for bandaging broken bones. 
Strips of cloth are covered with a milk of plaster of Paris 
and placed around the limb. As the excess of water 
evaporates, the CaS04, 2 H2O forms a stiff support which 
later must be broken to remove it. In making plaster 
casts harder, a solution of alum or borax is mixed with the 
plaster of Paris. More time is then required in the setting. 
As plaster of Paris is porous, it is often covered with melted 
paraffine or painted with a solution of paraffine in benzene 
to render it impervious. Stucco is plaster of Paris mixed 
with glue. When heated above + 160°, it does not com- 
bine readily with water again, and is said to be "dead 
burned." Plaster of Paris is used as an indirect fertilizer. 
Prepared artificially (by precipitation with an alkaline 
sulphate), it is a white powder, slightly soluble in water. 
When gypsum is dissolved in natural waters, a "perma- 
nent hardness " of the water is produced. 

Barmm Sulp/mte, heavy spar, "barytes," BaSO^, oc- 
curs naturally as a hard crystalline mass. When ground 
up, it is used to give weight to paper, paint, and so forth. 
Artificially prepared, it is a heavy, white powder, and pos- 
sesses distinct value in making paints. There is no ob- 
jection to its use for this purpose if it is sold under its own 
name and not as white lead. It is extremely insoluble in 
water (i : 350,000). 

Zinc Sulphate, white vitriol, ZnSO^, 7 H2O, is soluble in 
water. It is used as an emetic (depressant), yet it is poison- 
ous. It is also used in some forms of galvanic batteries. 

Mercuric SulpJiate, HgS04, is a white, soluble, crystalline 
salt which is used in some batteries, as Clark's standard 



THE SULPHATES. ALUMS 293 

cell. It usually changes and darkens on exposure to 
light. It hydrolyzes on standing in water, forming a 
basic sulphate, 2 HgO,HgS04. 

MerciLTous SuIpJiatc, Hg2S04, readily forms basic salts 
on the addition of water. 

Sulphates of Group III 

Al?iimn?nn Sulphate^ Al2(S04)3, 18 H2O, may be rendered 
anhydrous by heating, but ordinarily it is a white powder, 
soluble in water. This sulphate readily combines with the 
sulphates of the alkali group, molecule for molecule, to 
form an important class of bodies known as 

TJie Alums. These have the typical formula, M"^2(S04)3, 
N^2S04,24H20, or M"^NXS04)2, 12 H2O. M may be 
equivalent to Al, Fe, Cr, and so forth, and N to Li, Na, K, 
Rb, Cs, and NH^, or an organic derivative of ammonium. 
The name of the trivalent element is prefixed to designate 
the alum, as for example, chrom-potassium alum, Cr2(S04)3, 
K2SO4, 24 H2O. 

Potassium Alum, Al2K2(S04)4, 24 H2O, occurs in nature 
and has been known for a long time. The pure form is 
known as Roman alum. It is found dissolved in alum 
waters and may be made from alum shales (aluminum 
silicates containing much iron pyrites) by roasting, so that 
aluminum sulphate or ferrous sulphate is formed. These 
are dissolved in water, the ferrous sulphate crystallized out 
on concentration, potassium sulphate then added, and the 
alum crystallized out on further evaporation. Potassium 
alum dissolves in eight parts of cold water and one third 
part of boiling water, from which it may be obtained in 
fine large crystals. Ammonium Alum resembles potassium 
alum. Sodium Alum deliquesces and does not crystallize 
well. 



294 GENERAL INORGANIC CHEMISTRY 

Properties of the Alums. Potassium and ammonium alum 
crystallize easily and do not readily absorb water. They 
are used medicinally, and in the place of aluminum sulphate 
in tanning and sizing paper, as they have the property of 
rendering gelatin insoluble. Paper when first made is 
porous. When treated with glue (gelatin) and an alum so- 
lution, and passed between hot rollers, the surface becomes 
impervious, and ink is not absorbed. The alums are also 
used as mordants in dyeing. When coloring matters are 
precipitated with alums, '' lake dyes " are obtained. Alums 
are used in purifying waters for drinking purposes, as they 
readily hydrolyze in dilute solution. The gelatinous alum- 
inum hydroxide formed incorporates not only the sus- 
pended impurities, but many of the substances dissolved 
in the water. It incorporates a large proportion of the 
bacteria present and settles as a jelly. The purified water 
may then be drawn off, or, as is more usual, the jelly is 
separated by filtration. The alums have been used in mak- 
ing cheap baking powders, but as alum is an astringent, 
such use is objectionable in foods, as it interferes with the 
digestive processes. 

Sulphates of the Remaining Groups 

Lead Sulphate, PbSO^, is a white, quite insoluble, crystal- 
line substance which is used as a pigment in making 
paints. A basic lead sulphate, 2 PbO,PbS04, known as 
" white sublimed lead," is used extensively as a pigment 
in the place of ordinary "white lead." On account of the 
insolubility of lead sulphate, the antidote for lead poison- 
ing is a soluble sulphate. 

Ferrous Sulphate, copperas, green vitriol, FeS04, 7 H2O, 
is a green, crystalHne substance, soluble in water, and poi- 
sonous. It is decomposed by heat. It is used medicinally 



THE SULPHATES. ALUMS 295 

and as a disinfectant, or rather as a deodorant. It is also 
used in tanning, dyeing, and making inks. 

Ferrous sulphate, as well as the sulphates of other 
bivalent positive elements, as Mn, Co, Ni, Mg, and so 
forth, form a series of double salts with the sulphates of 
the alkali metals with the type formula, M"N^2(S04)2, 
6 H2O. These all crystallize in monoclinic tables. 

Ferric Sulphate, Fe2(S04)3, is a deliquescent, yellowish 
solid which is used medicinally. 

EXERCISES 

1. Tabulate the formulas of the following: soda alum, Roman 
alum, ammonium-iron, potash-chromium, rubidium-manganese, 
and caesium alums. 

2. Complete the equations : — 

(i) NaHCOg -f AIK2(S04)4, 24 H^O z> 
(2) Na.S04-f-Pb(NO,)2Z± 



CHAPTER XLVI 

OTHER OXIDES OF GROUP VI, AND THEIR DERIVATIVES 

Negative Series 

SO2 H2SO3 SO3 H2SO4 

SeOa . H2Se03 H2Se04 

Te02 H2Te03 Te03 H2Te04 

Seleniitin Dioxide, Se02, is prepared by burning sele- 
nium in the air or by oxidizing it with nitric acid. It forms 
white crystals which volatilize at -1-320°, has a peculiar 
disagreeable odor, and is dehquescent. 

The hydroxide, SeO(OH)2, or Selenions Acid, H2Se03, 
is prepared by oxidizing selenium with nitric acid. It is 
easily reduced, yielding selenium. Selenious acid is dibasic 
and forms selenites, which are also easily reduced. When 
heated on charcoal, they give the odor of decayed horse- 
radish. 

Seleiiic Acid, H2Se04, is obtained by the strong oxida- 
tion of selenium : - — 

Se + 3 CI2 + 4 H20= H2Se04-F6 HCl. 

It has not been entirely freed from water. It decomposes 
at -1-280° into oxygen and selenious acid. It is a colorless, 
very acid liquid, which forms the selenates, analogous to the 
sulphates. 

TelbLriinn Dioxide, TeOg, occurs in nature. Tellurous 
Acid, H2Te03, is a light white powder, slightly soluble in 
water, which forms tellurites. 

296 



OTHER OXIDES OF GROUP VI, AND DERIVATIVES 297 

TelliLriiim Trioxide, TeOg, is obtained by heating telluric 
acid. It is a yellow, crystalline mass which is decomposed 
when strongly heated. 

Telluric Acid, H2Te04, is prepared by fusing tellurium 
or tellurium dioxide with potassium carbonate and an oxi- 
dizing agent, as potassium nitrate, and setting the acid free 
by means of a stronger one. 

Positive Series 

CrO Cr(OH), Cr.O. Cr,(OH),; CrO, CrOg CrOo(OH)2 

MoO Mo.Og M0O.2 M0O3 Mo02(OH)2 

WO, WO3 WO. (OH), 

UO, U(OH),UOo UO,(OH)2 

Besides these, there are many compounds of more com- 
plicated formulas. 

CJironiiiim Monoxide, chromous oxide, CrO, is not known 
free from water. The hydroxide, Cr(0H)2, is a yellow 
precipitate produced by adding a soluble hydroxide to a 
chromous solution, as CrCl2. On the removal of water, 
the oxide is formed. It is readily oxidized by the oxygen 
of the air. When the hydroxide is heated it gives off 
hydrogen : — 

2 Cr(0H)2= Cr203 + H2O + H2. 

The chromous salts are obtained by reduction of the 
chromic compounds, generally by heating in hydrogen. 
They absorb oxygen with avidity at ordinary temperatures. 

Chromium Sesqinoxide, chromic oxide, Cr203, is found in 
nature as chromic iron ore, Cr203, FeO. It is the most 
stable of the chromium oxides, and is prepared artificially 
by heating the hydroxide, Cr(OH)g. It is a green powder, 
specific gravity 5.21, and is almost insoluble in acids, 
especially after intense heating. It is used in coloring 



298 GENERAL INORGANIC CHEMISTRY 

glass and porcelain green, and as a green pigment. It 
does not give as live a color, however, as do the copper 
arsenites. 

CJirommm Hydroxide ^ Cr(OH)3, is precipitated as a ge- 
latinous, greenish blue compound from solutions of triva- 
lent chromium compounds : — 

CrClg + 3 NaOH it 3 NaCl + \ Cr(OH)3. 

It dissolves in an excess of the fixed alkaline hydroxides. 
This would indicate acidic character, which is more evident 
when it is partially dehydrated : — 

Cr(0H)3 = CrO, OH -f H.p, 

from which are derived the chromites. For example, if 
the hydrogen is replaced by iron, we have Fe(0,OCr)2, 
or FeO, Cr203, chromic iron stone, chromite, ferrous 
chromite, the important occurrence in nature. If two 
molecules of the hydroxide have one molecule of water 
removed, we have Qx^O{OY{)^, a brilliant green powder, 
known as Guignet's green, which is used as a pigment. 
The substance is made commercially by an indirect method 
and not as stated above. 

Chromium hydroxide is soluble in the ordinary acids, by 
which conduct it exhibits its basic character. The normal 
chromium salts, as the sulphate, Cr2(S04)3, the chloride, 
CrClg, and so forth, are derived from this compound. 
They are quite stable toward oxygen, and are usually 
purple or violet in color. The sulphate, Cr2(S04)3, forms 
alums. They are used in dyeing and tanning. By heat- 
ing a water solution, which is usually purple, it is changed 
into a green basic salt, which on standing in the cold 
changes back to purple. 

Chromium Trioxide, CrOg, is prepared by fusing Cr203 



OTHER OXIDES OF GROUP VI, AND DERIVATIVES 299 

with an oxidizing agent, as Na202. A yellow mass of a 
chromate is obtained which is leached with water. The 
soluble chromate is decomposed by concentrated sulphuric 
acid, and the trioxide crystallizes in long red needles on 
cooling. When heated it melts to a red liquid, being de- 
composed at + 250° : — 

2 CrOg = Cr203 + O3. 

It is easily reduced to the sesquioxide by means of organic 
or other reducing matter. It possesses a powerful oxidiz- 
ing action, and is often used as an oxidizing agent in an 
aqueous solution. Mixed with concentrated sulphuric acid 
it exhibits an extremely powerful oxidizing action. This 
is very pronounced in the presence of organic matter. 
The long, red rhombic crystals are deliquescent. With 
water, in which it is very soluble, it appears to form 
chromic acid, H2Cr04, which is not actually known, but a 
number of salts are derived from it. The solution has an 
acid taste and is- an astringent. It dyes silk, skin, and 
wool yellow. 

When alkaline hydroxides are added to a water solution of 
CrOg, the CJiromatcs, MgCrO^, and Dichi'oinates, M2Cr207, 
are formed. They are usually prepared, however, directly 
from the alums and are used in the preparation of other 
chromium compounds. 

Potassium Chromate, K2Cr04, is a yellow, crystalhne 
salt, soluble in water. It is decomposed by strong acids 
to form dichromates : — 

2 K2Cr04 + H2SO4 = K2Cr207 + K2SO4 -f- H2O. 

When potassium hydroxide is added to the dichromate, 
the chromate is re-formed : — • 

KXr.O^ + 2 KOH = 2 K.CrO^ + H,0. 



300 GENERAL INORGANIC CHEMISTRY 

Potassmm Dichromate, red chromate of potash, KgCrgO^, 
is manufactured on a large scale from sodium dichro- 
mate : — 

Na^Cr^O^ + 2 KCl = Y.f.xf).^ + 2 NaCl. 

It crystallizes in large, red triclinic prisms, which are sol- 
uble at ordinary temperatures in 10 parts of water. When 
heated it decomposes with the liberation of oxygen : — 

2 K2Cr207 = 2 KgCrO^ + Cr203 + O3. 

It is used in the manufacture of pigments, in photography, 
and in galvanic batteries. 

Lead Chromate, chrome yellow, PbCrO^, resembles the 
sulphate in solubility in water. It is extensively used as 
a pigment. Pigments with- intermediate shades from yel- 
low to orange are had with various proportions of the basic 
chromate [PbO, PbCr04], which is orange. 

Magnesium Chromate, MgCrO^, 7 HgO, has the type of 
the sulphate, Epsom salts. 

When some of the chromates are treated with acids, 
they form polychromates : — 

K2Cr207 + 4 H2SO4 = Cr2( 504)3, K2SO4 + 4 H2O + 3 O. 

CJirom^iiLm Sulphides. Cr2S3 is a black substance, pre- 
pared by a fusion method. It is not obtained by ordinary 
precipitation methods. When ammonium sulphide is 
added to chromium sulphate solution, chromium sulphide 
is not formed, but the hydroxide : — 

Cr2(S04)3+3(NH4)2S + 6 H2O = z{^n,\SO, + Cr2S3, but 
Cr^Ss + 6 H2O = 2 Cr(OH)3 + 3 H2S. 

Molybdemtm Trioxide, M0O3, is an acid-forming oxide 
which appears to form molybdic acid, HgMoO^. Lead 



OTHER OXIDES OF GROUP VI, AND DERIVATIVES 301 

Molybdate, wulfenite, PbMoO^, is an important ore of 
molybdenum. Molybdic acid resembles chromic and silicic 
acids in forming polymolybdates, as for example, Na2Mo04, 
NagMogO^, Na2Mo30io, . . . Na2MoioOi3. It also forms 
" complex " acids and salts ; for example, a brilliant yellow 
precipitate, with the composition (NH4)3P04, 12 M0O3, 
6 H2O, is produced by bringing soluble molybdate and 
phosphate solutions together. It is insoluble in nitric acid, 
but readily soluble in ammonium hydroxide. This com- 
plex serves as a satisfactory material to separate the phos- 
phoric acid from iron and aluminum compounds in making 
analyses of phosphates. 

Molybde7min SidpJiide^ MoS, occurs in nature as molyb- 
denite. 

Tungsten Trioxide, WO3, is a yellow powder which 
resembles M0O3 ^^ ^^^ chemical conduct. The ttmgstates, 
as (FeMn)W04 (wolframite), CaW04 (scheeHte), and 
PbW04 (stolzite), are the chief tungsten minerals and 
appear to be derived from tungstic acid, H2WO4. A num- 
ber of poly tungstic acids are known. A derivative of one 
of them, K2W4O12, is known as '* tungsten bronze." As 
an illustration of the complexity of some of these 
substances, the determined formula of one may be 
given (E.F.Smith): 18 BaO, VO2, V205,8 P205,6o WO3, 
150H2O. 

Uraiiiiiin Dioxide, UO2, enters into some compounds, as 
(UO2), (N03)2, ^^^'<^JV^ nitrate. The uranyl salts exhibit 
splendid greenish yellow fluorescence. 

Uranium Trioxide, UO3, is acid-forming. Uranic acid, 
H2UO4, forms pjly-uranates similar to the poly-compounds 
of the other members of this series. 

Uraninite, pitchblende, UgOg, appears to be a uranic 
uranate, U(U04)2. 



302 GENERAL INORGANIC CHEMISTRY 

EXERCISES 

1. Complete the reaction : — 

K2Cr04+Pb(N03)2^ 

2. Write the reactions showing the changes from each chromium 
oxide and hydroxide to the other. 



CHAPTER XLVII 
OXIDES OF THE NEGATIVE MEMBERS OF GROUP VII 

No compound of fluorine with oxygen has yet been ob- 
tained. Three oxides of chlorine are known ; namely, the 
monoxide (CI2O), the tetroxide (CI2O4, or ClOg), and the 
heptoxide (CI2O7). Bromine has not as yet yielded pure 
compounds with oxygen, although three hydroxy-com- 
pounds, or oxyacids, are known. Iodine forms the 
tetroxide (I2O4) and pentoxide (IgO^). These compounds 
and the oxyacids are tabulated below. 

C120 HOCl HOBr HOI 

CI2O3 HOCIO 



CIO2* I2O4 

CI265 HOCIO2 H0Br02 I2O5 HOIO2 

CI2O7 HOCIO3 HOBrOg HOIO3 

When chlorine is brought into contact with freshly pre- 
pared dry mercuric oxide, this reaction occurs : — 

HgO + 2 CI2 = HgC]2 + C120. 

Chlorine Mo7ioxide, ClgO, is a reddish yellow gas, with a 
specific gravity of 3, which is readily condensed to a liquid. 
Both the gas and the liquid are unstable, exploding on 
warming. They are powerful oxidizing agents and exhibit 
their explosive properties when any oxidizable substance, 

* CIO2 is actually recognized. This may or may not be a mixture of CI2O3 
and CI2O5 existing as CI2O4. 

7PZ 



304 GENERAL INORGANIC CHEMISTRY 

such as organic material, is present. The gas is readily 
soluble in water, forming hypochlorous acid : — 

CI2O + H2O = 2 HOCl. 

Hypochlorous Acid, HOCl, which is known only in a water 
solution, is best obtained by another reaction, which is re- 
ferred to below. It is a powerful oxidizing agent, and is 
one of the most important commercial bleaching agents. 
The bleaching action of chlorine may be accounted for 
by the formation of hypochlorous acid, for, in the absence 
of water, it exhibits only very weak bleaching properties. 
When chlorine is dissolved in water, a reversible reaction 
takes place : — 

CI2 + H20:;!:HCl-f HOCL 

Equilibrium soon occurs. If one of the products is removed, 
the equilibrium is destroyed and the reaction proceeds, as 
is usual, in a direction to re-establish the equilibrium. For 
example, if mercuric oxide, HgO, is present, the HCl com- 
bines with it to form HgCl2- Hypochlorous acid, HOCl, 
is a weak acid, and has practically no action upon the mer- 
curic oxide, hence it remains in solution. Therefore, if we 
suspend HgO in water and lead in chlorine, this reaction 
takes place : — 

HgO + H2O + 2 CI2 = HgCl2 + 2 HOCL 

If a dilute solution of an alkaline oxide, essentially alka- 
line hydroxide, is present, both acids are neutralized : — 

2 KOH + CI2 = KCl 4- KOCl + U^O. 

A solution of a chloride and hypochlorite in equal 
molecular proportions is obtained. When KOH is used, 
the solution is called '' eau de Javelle " ; when NaOH, 
** Labarraque's solution," or " chlorinated soda." Both 



OXIDES OF NEGATIVE MEMBERS OF GROUP VH 305 

solutions are strong disinfecting and bleaching agents. If 
chlorine is passed into a solution of limewater or over 
nearly dry slaked lime, this reaction occurs : — 

2 Ca(0H)2 + 2 CI2 = CaCl2 + Ca(0Cl)2 + 2 H2O. 

The product is known as " bleaching powder," or 
*' chloride of lime," to which the formula CaGl(OCl) is 
usually assigned. It is an important article of commerce, 
as it serves as one of the most convenient means for trans- 
porting chlorine. This becomes clearer if we consider the 
conduct of HOCl under variable conditions. 

Hypochlorous acid when heated, especially in sunlight, 
decomposes : — 

2HOCl=2HCl + 02. 

This accounts for the evolution of oxygen from chlorine 
water when it is exposed to sunlight. The reaction is 
accelerated by some catalytic agents, as cobalt oxide. 

When hypochlorous acid, or a hypochlorite, is mixed 
with an acid, chlorine is evolved : — 

HOCl + HCl:^H20 + Cl2; or 
CaCl(OCl) + H2S04^CaS04 + HOCl + HCl ; or 
2 CaCl(OCl) + H2O + COs^CaCOg + CaCl2 + 2 HOCl. 

The last reaction calls attention to the readiness with 
which bleaching powder decomposes. It should not be 
kept in tightly closed casks, as the gases are liberated by 
this reaction and the vessel is liable to burst. Pure chlo- 
ride of Hme contains about 49 per cent of available chlorine. 
A good grade contains 25 per cent. It is extensively used 
for disinfecting and bleaching. In the latter it is more 
generally applied to vegetable fibers, as it is injurious to 
silk and wool. In any event, Ihe excess used should be 



3o6 GENERAL INORGANIC CHEMISTRY 

removed by subsequent treatment with an " anti-chlor," 
such as sodium thiosulphate. 

Hypobromotis Acid^ HO Br, and the Hypobromites are 
prepared in the same manner. They are used for the 
same purposes as the hypochlorites but to a less extent. 
Both react with ammonia or substituted ammonia com- 
pounds as follows : — 

3 NaBrO + 2 NHgi^ 3 NaBr + 3 H2O + t N2 ; 
3 NaBrO + CO(NH2)2:^3 NaBr+ 2 H2O +| N2 + CO2. 

The last reaction is frequently used to determine the 
amount of urea [CO(N 112)2], ^^^ ^^ ^^^ ^v^-dX products of 
nitrogenic metabolism of animals, discharged in the urine. 
The hypobromite solution is made with an excess of 
sodium hydroxide, which combines with the carbon dioxide 
generated. The sodium bromide is soluble in the w^ater 
present. The nitrogen is not dissolved, so it is collected 
and measured. 

When solutions of hypochlorous or hypobromous acids 
are concentrated, or their salts heated, a part is oxidized 
and a part reduced: — 

3 HOCl = HOCIO2 + 2 HCl, or 
3 KOCl = KOCIO2 + 2 KCL 

The Chlorates, as KCIO3, salts of Chloric Acid, HOCIO2, 
may be made by passing chlorine into a concentrated solu- 
tion of caustic potash warmed to about + 90° : — 

3 CI2 + 6 KOH = 5 KCl + KCIO3 + 3 H2O. 

Potassium Chlorate, KCIO3, the most important chlorate, 
crystallizes out from the above solution first in large, white 
tabular crystals. Technically, calcium chlorate is usually 
made first and that treated with potassium chloride : — 

Ca(C103)2 + 2 KCl = CaCl2 + 2 KCIO3. 



OXIDES OF NEGATIVE MEMBERS OF GROUP VII 307 

It is also made now by electrolysis of a solution of potas- 
sium chloride. It has a cool, astringent taste ; it is used 
medicinally, in the preparation of oxygen, and in explo- 
sives. When a chlorate is heated, or pulverized with 
organic or combustible matter, it undergoes rapid de- 
composition. This has frequently resulted in violent ex- 
plosions, hence the utmost care should be exercised in 
handling chlorates. 

CJdoric Acid, HCIO3, is obtained by the action of sul- 
phuric acid upon barium chlorate : — 

Ba(C103)2 -f H^SO^r^l BaSO^ -f 2 HCIO3. 

The liquid must be concentrated under diminished pres- 
sure, as it decomposes above + 40°. A 40 per cent solution 
has a specific gravity of 1.28. This acid and the chlorates 
are decomposed by hydrochloric acid : — 

HCIO3 + 5 HCl = 3 H^O -f- 3 CV 

Chloric acid would appear to be the hydroxide derived 
from CI2O5 : — 

Cl205+H20 = 2HC103; 

but when a chlorate is treated with cold concentrated 
sulphuric acid, a heavy, dark yellow gas is obtained, which 
may be condensed to a brown-red liquid. This is known 
as cJilorine tetroxide, CI2O4, or C102- The liquid becomes 
a solid at — 79° and boils at + 10°. It has a pecuhar 
odor, and when heated to -f 30° explodes. It is a power- 
ful oxidizing agent, setting fire *to sugar or similar organic 
matter as soon as they come in contact. 

As has been suggested, CI2O4 may really be a compound 
or mixture of CI2O5 and CI2O3, for when dissolved in water 
this reaction takes place : — 

CI2O4 + H2O = HCIO3 + HCIO2. 



3o8 GENERAL INORGANIC CHEMISTRY 

Chlorotis Acid, HCIO2, may also be formed by dissolving 
CI2O3 in water : — 

Cl203+H20 = 2HC102. 

Certain salts as AgC102 and Pb(C102)2 are known. 

If an organic substance, such as oxalic acid, H2C2O4, 
is present during the production of chloric acid by the 
method given, a green gas with a very pungent, irritating 
odor is generated. This is Chlorine Trioxide, CI2O3, which 
is very unstable, being decomposed by heat, light, or 
organic matter. 

Bromic Acid, HBrOg, and the Broinates are prepared in 
the way that the corresponding chlorine compounds are 
made, except that no bromine oxides are known. 

If iodine is treated with a strong oxidizing agent, it 
changes into a white powder, known as Iodine Pentoxide, 
I2O5. On heating, this decomposes into iodine and oxygen, 
hence it possesses strong oxidizing properties. It dis- 
solves in water to form iodic acid : — 

I205 + H20 = 2HI08. 

Iodic Acid forms salts, as sodium iodate, NalOg, which 
sometimes are found in natural beds of sodium nitrate. 
The acid has strong oxidizing and bleaching properties. 
It serves to show the influence temperature and concen- 
tration play in the rate of reactions. When water solutions 
of iodic acid and sulphur dioxide are mixed, this reaction 
occurs : — 

2 HIO3 + 5 SO2 4- 4 H2O = 5 H2SO4 + I2. 
Free iodine colors starch blue ; therefore, if a few drops 
of a starch solution are added, the moment the reaction 
occurs the colorless solutions become blue. If proper 
amounts of solutions of definite strength are taken, the 
actual time for the reaction is regular for each experiment. 



OXIDES OF NEGATIVE MEMBERS OF GROUP VII 309 

The time changes with the change of strength or the 
temperature. 

PcrcJiloric Acid, HCIO4, is formed by the decomposition 
of chloric acid : — 

2 HCIO3 - HCIO2 + HCIO4. 

It is usually prepared by treating barium perchlorate 
with sulphuric acid : — 

Ba(C104)2 + H2SO4 = BaSO^ + 2 HCIO^. 
It is a mobile, colorless liquid, with a specific gravity of 
1.78. It can be preserved but a short time, and then only 
in the dark. It is a powerful oxidizing agent, and sets 
fire to paper and wood at once, and causes severe wounds 
when brought in contact with the skin. It appears to be 
the hydroxide of cJilorine heptoxide, Cl20y, about the exist- 
ence of which there is some question. 

When potassium chlorate is heated just to fusion, a de- 
composition occurs as follows : — 

2 KCIO3 = KCIO4 + KCl + O2. 

The P erchlo7'ates are sometimes found in natural niter, 
but it should be removed before the nitrate is applied as 
fertilizer, for it is injurious to plants. On treating per- 
chloric acid with iodine the chlorine is displaced : — 
HCIO4 4- I = HIO4 + CI. 

Periodic Acid, HIO4, is a colorless, crystalhne, dehques- 
cent solid. It decomposes when heated to + 140° and 
possesses a powerful oxidizing action. The periodates are 
prepared by heating the iodates. . 

EXERCISES 

1. Arrange in tabular form the properties of the oxides and 
hydroxides of chlorine. 

2. Contrast the conduct of chlorine, bromine, and iodine with 
the hydrogen and the hydroxy-compounds of those elements. 



CHAPTER XLVIII 

OXIDES AND SULPHIDES OF MANGANESE 

Manganese resembles chromium and iron not only in 
physical properties, but in the number and variety of its 
oxygen compounds and their derivatives as well. There 
are also striking resemblances between some of its com- 
pounds and some of the halogen compounds. This is 
especially the case in the number and variety of the 
oxygen compounds of manganese and chlorine, and the 
resemblance in chemical conduct of their derivatives. 

Manganese shows greater variation in valence towards 
oxygen than any other element known. It forms MnO, 
MngO^, Mn203, MnOa, MnOg, and Mn207. The monoxide 
and sesquioxide are base-forming ; the last two are acid- 
forming, while the dioxide is weakly so ; and MngO^ may 
be regarded as neutral ; it is the most stable. Some of the 
oxides occur in nature and constitute the main sources of 
manganese. 

Manganese Monoxide^ MnO, is obtained by heating the 
higher oxides in hydrogen. It is a stable, greenish 
powder which forms manganous salts with acids ; for 
example, MnCl2, Mn(N03)2, and MnSO^. These are the 
chief salts containing manganese as a base. As a rule, 
they are pink colored and stable in acid solutions, but 
absorb oxygen readily in the presence of alkalies. The 
sulphate (MnS04), nitrate [Mn(N03)2], and chloride 
(MnClg) are stable, crystalline compounds. 

310 



OXIDES AND SULPHIDES OF MANGANESE 311 

When solutions of these salts, for they are all soluble in 
water, are treated with an alkaline hydroxide, this reaction 
takes place : — 

MnCl2 + 2 NaOH => 2 NaCl + j Mn(0H)2. 

Manganous Hydroxide, Mn(OH)2, is a white gelatinous 
compound which rapidly becomes brown on exposure to 
air, due to oxidation. 

Manganese Sesq?noxide, manganic oxide, Mn203, occurs 
in nature as braunite. With dilute hydrochloric acid it 
forms MnCl2, and Mn02 is produced. If the acid is con- 
centrated, all of the manganese forms MnC]2, and CU is 
evolved. With fairly concentrated sulphuric acid, it forms 
the manganic salt, Mn2(S04)3, which is purple-red in color. 

When these are precipitated from a water solution by an 
alkaline hydroxide, a brown-red hydroxide is obtained : — 

Mn2(S04)3 + 6 NaOH 1^3 Na2S04 + 2 Mn(OH)3. 

This hydroxide readily loses a molecule of water, and 
MnO, OH is formed. This brown compound is found in 
nature as manganite and resembles metaluminic acid in its 
conduct. 

Manganojis-manganic Oxide, Mn304, occurs in nature as 
hausmannite. It is produced when any of the oxides are 
heated in the air. It gives no salts with acids nor does it 
form an oxyacid. It may be looked upon as the manga- 
nese salt of metamanganous acid, Mn(OMnO)2, or the 
manganese salt of orthomanganic acid, Mn2Mn04, as it 
shows no resemblance to the spinels. 

Manganese Dioxide, black oxide of manganese, Mn02, 
occurs in nature as the mineral pyrolusite. It occurs 
widely distributed and in fair amounts, but in pockets, 
hence the extent of a deposit cannot be foretold. It is 



312 GENERAL INORGANIC CHEMISTRY 

the chief ore of manganese. It is formed when oxidizing 
agents are added to the manganous salts in solution. It 
is used in preparing oxygen and chlorine, as a depolarizer 
in Leclanche cells, and in "bleaching" and coloring glass 
(washing by fire). It combines with certain positive oxides 
to form manganites ; a complicated one is KgMngOii. They 
are very little understood, however. 

Manganic Acid, HgMnO^, would correspond to the tri- 
oxide, MnOg, but no such compound is known to exist in the 
pure form. Nor is the acid known in the free state. Its 
compounds, as the manganates, for example, NagMnO^, are 
prepared by fusing the dioxide with an alkaline hydroxide 
and some oxidizing agent, as potassium chlorate or sodium 
dioxide. These compounds are unstable, unless a large 
excess of alkali is present. The alkahne manganates give 
a green solution in water, which is decomposed by carbon 
dioxide or by dilution on exposure to the air. They are 
strong oxidizing agents, and are used as disinfectants. 
When a dilute acid is added to the green solution, it 
becomes pink, due to the formation of the permanganate, 
NaMnO^. Carbon dioxide produces the same change. 

Manganese Heptoxide, MugO^, is obtained by adding cold 
concentrated sulphuric acid to potassium permanganate. 
It is a dark oily liquid, very unstable, which decomposes 
violently on warming or on coming in contact with organic 
matter, in the same way that the oxides of chlorine do. 

Permanganic Acid, HMn04, may be prepared by add- 
ing dilute sulphuric acid instead of the concentrated acid 
used in the last reaction. It is a red Hquid which is 
decomposed by heat and organic matter. It is a powerful 
oxidizing agent, whose chief salt is potassium perman- 
ganate, KMn04. This is prepared from potassium man- 
ganate by passing carbon dioxide through a solution of it, 



OXIDES AND SULPHIDES OF MANGANESE 313 

which changes from green to red. On evaporation of the 
solution, dark purpHsh red crystals are obtained which 
dissolve in water and g z a. purple or pink solution. It is a 
powerful oxidizing agent, and is used as a disinfectant. 
The permanganates correspond to the perchlorates. 

When a permanganate is mixed with dilute sulphuric 
acid in the presence of oxidizable matter, the permanganate 
is decomposed with the liberation of oxygen and the loss 
of the characteristic color: — 

2 KMnO^ + 3 H2SO4 = K2SO4 + 2 MnSO^ + 3 H^O 4- 5 O. 

If iron sulphate, in the ferrous form, is present, it is at 
once oxidized to the ferric condition : — 

2 KMnO^ + 10 FeSO^ + 8 H^SO^ = K2SO4 + 2 MnSO^ 

This reaction is extensively used to determine the amount 
of iron in a solution of unknown strength. Permanganates 
are also decolorized by sulphur dioxide, hydrogen dioxide, 
and oxalic acid : — 

2 KMnO^ + 5 SO2 + 2 H2O = K2SO4 + 2 MnSO^ 
V2H2SO4; 

2 KMn04 + 5 H2O2 + 3 H2S04= K2SO4 + 2 MnSO^ 
^ V 8 H2O 4- 5 02"^; 

2 KMnO^ 4- 5 C2H2O4 + 3 H2SO4 = K2SO4 + 2 MnS04 

4- IoC02 + 8H20• 
Two S2ilpJiides of manganese, MnS and MnSg, are found 
in nature. The monosulphide is flesh-colored and is formed 
by precipitating a manganous salt solution by an alkaline 
sulphide: — 

Mna2 4-(NH4)2S^2NH4Cl4->^MnS. 



314 GENERAL INORGANIC CHEMISTRY 

A three-fourths sulphide, MngS^, corresponding to the 
neutral oxide, Mn304, is also known. 

EXERCISES 

1. Complete the reaction for xMnoO^-j-yHCl = wMnC\2 + 

2. Complete the equation : ;v:Mn304 +j'HCl = 7£/MnCl9 -{- 

3. How many cubic centimeters of a solution of potassium per- 
manganate, which contains 40 grams to the liter, would be neces- 
sary to oxidize 0.5 gram of iron from the ferrous to the ferric 
condition? 

4. How much iron is present in a solution which requires 47 c.c. 

of a — solution of KMn04 to produce a pink color? 
4 



CHAPTER XLIX 
OXIDES AND SULPHIDES OF GROUP VIII 

The oxides of this group are given in tabular form below : 



Pd.O 



FeO 


Fe.Oo 


Fe,0, 




(i'eO,) 






CoO 


Co",03 


Co,p^ 










NiO 


NiA 










NiO^ 


RuO 


Rll.Pg 




RuO, 


(RUO3) 


Ru,0; 


RUO4 


RhO 


Rh.Og 




RhO., 








PdO 






PdO, 










Sm,03 
EliJo, 












OsO 


Gd,0, 

OS.Og 




OsO, 


OsO.3 




OSO4 


IrO 


Irp. 




IrO, 








PtO 


Pt'^Oo 




Ptd> 









It will be noted that, although the type oxide of this 
group is MO4, only three have been obtained, and these 
are quite unstable. Two-thirds oxides, MgOg, are known 
for all of them with the exception of palladium. Mon- 
oxides, MO, are known for all except those of the gadolin- 
ite subgroup. The two platinum subgroups form MO2. 
Salts (-ous) are derived from the monoxides, as cobaltous 
chloride (CoClg) and platinous chloride (PtC]2). Salts (-ic) 
are had from the sesquioxides of the iron and gadolinite 
subgroups, as ferric chloride (FeClg) and europic chloride 
(EuClg); and from the dioxides of the platinum subgroups, 
as palladic chloride (PdCl4) and platinic chloride (PtCl4). 

Ferrous Oxide, FeO, is prepared by heating ferric oxide 
with hydrogen at + 500°. It is a black powder which 
readily takes up oxygen. 

315 



3i6 GENERAL INORGANIC CHEMISTRY 

Ferrous Hydroxide, Fe(0H)2, is obtained by the precipi* 
tation of a ferrous salt by an alkaline hydroxide as a gelat- 
inous white solid, which is usually seen with a dirty green 
color. In its preparation it is necessary to exclude 0x3^- 
gen, as it is readily oxidized from the green to the red- 
brown ferric hydroxide. It forms a series of ferrous 
salts, the sulphate, FeS04, 7 H2O, copperas, being the 
most important one. It forms double salts, as FeSO^, 
(NH4)2S04, 6 HgO (Mohr's salt), which is used in making 
ink and dyes. 

Ferric Oxide, iron sesquioxide, Fe203, occurs naturally 
as hematite, the most important ore of iron. It is found 
as a powder, mixed with more or less clay as red ocher. 
It is formed by heating the hydroxide or any salt of iron 
in which the acid is volatile. When made by heating the 
sulphate, it was called calcothar and Venetian red. It is a 
heavy, brownish red powder, insoluble in water and diffi- 
cultly soluble in acids, especially after it has been ignited. 
In compact form, as when made by burning pyrites or 
igniting the natural hydrated oxide, it is known as ruddle. 
The cinder from the burning of pyrites is largely Fe203= In 
addition to its enormous use for making iron, some forms 
are used as "mineral paint," and others for polishing steel, 
glass, and so forth. 

Ferric Hydroxide, Fe(0H)3, is a reddish brown precipi- 
tate produced by the addition of an alkahne hydroxide to 
a ferric salt, as Fe2( 804)3 : — 

Fe2(S04)3 + 6 NaOH7>3 Na2S04 -h |2 Fe(OH)3. 

This is only one of the several hydroxides which are 
known more or less and which occur in nature under the 
names of brown hematite, limonite, goethite, and impure 
bog iron ore. Mixed with clay, they give yellow ocher 



OXIDES AND SULPHIDES OF GROUP VIII 317 

and constitute the coloring matter of many soils. Red 
och'er may be made by heating the yellow ocher. Iron 
rust is a mixture of these hydroxides. The normal hydrox- 
ide, Fe(OH)3, when freshly made, is soluble in acids, giv- 
ing ferric salts. It is quite soluble in a ferric chloride 
solution. The chloride may be separated by dialysis, a 
blood-red colloidal solution of the hydroxide remaining 
behind. The solution is known as " dialyzed iron " and is 
used in medicine. On heating the solution, or on the addi- 
tion of an electrolyte, the hydroxide is precipitated. 

We may look upon Fe(0H)3, after it has been partially 
dehydrated, as having the formula FeO, OH. This com- 
bines directly with several oxides, as those of calcium, 
magnesium, iron, and zinc, whereby are derived the min- 
erals franklinite [Zn(Fe02)2] and magnetite [Fe(Fe02)2]. 

Ferrous -ferric Oxide, magnetic oxide, Fe304, occurs in 
nature as magnetite, or " lodestone." It usually contains 
some titanium. It is prepared in the laboratory by the 
union of iron and oxygen at high temperatures, as in the 
case of iron burning in oxygen or at the blacksmith's 
forge, when it is spoken of as '' blacksmith scales." It is 
a magnetic, neutral oxide from which no compounds are 
directly derived. It is found as black particles in many 
sands, from which it is easily separated by a magnet. 

Ferric Acid, H2Fe04, would correspond to the oxide 
FeOg, but no such oxide is known, nor is ferric acid known 
in the free state. Some of its compounds, however, are 
known, for when ferric hydroxide is suspended in an alka- 
line solution and is oxidized by chlorine, a purple solution 
is obtained from which K2Fe04 may be precipitated. 

Potassium Ferrate, K2Fe04, is also prepared by the 
fusing of iron with an oxidizing agent, as potassium 
nitrate. 



3i8 GENERAL INORGANIC CHEMISTRY^ 

Cobaltous Oxide, CoO, is prepared by reducing the 
higher oxides by means of hydrogen. It is a brown 
powder insoluble in water but soluble in acids, and forms 
cobaltous compounds, which are the principal salts of 
cobalt. The silicate, '' smalt," is largely used in mak- 
ing blue glass and as a blue pigment. The other chief 
salts are the nitrate, sulphate, and chloride, which, as a 
rule, are red, deliquescent bodies becoming blue when 
deprived of water. They are used as a basis of sympa- 
thetic ink. 

The Hydroxide, Co(OH)2, is obtained by precipitation 
with an alkaline hydroxide in the absence of oxygen. 

Cobaltic Oxide, C02O3, is obtained as a dark brown 
powder by heating the nitrate. When heated with alu- 
minium oxide, a cobalt ultramarine, or Thenard's blue, is 
prepared. If zinc oxide is used, a green cinnabar, or Rin- 
mann's green, is obtained. 

The Hydroxide, Co(OH)3, can be obtained by the pre- 
cipitation of cobalt salts with oxidizing agents. It is slightly 
basic, giving a few salts. 

Cobaltous -cobaltic Oxide, C03O4, is obtained as black 
oxide when other cobalt oxides are heated in the air. 

Indications point to the existence of cobaltic acid, simi- 
lar to ferric acid. Potassium cobaltate seems to be formed 
by fusing any of the oxides with caustic potash. 

Nickel Monoxide^ NiO, occurs in nature. It is prepared 
as a green powder by strongly heating the Jiydroxide, 
Ni(0H)2, which is precipitated by alkaline hydroxides 
from the solution of a nickelous salt. 

Nickel Sesqiiioxide, Ni203, is obtained as a black powder 
by gently heating nickel nitrate in the air. It is soluble 
in sulphuric and nitric acids, when oxygen is evolved, and 
in hydrochloric acid, when chlorine is given off. This 



OXIDES AND SULPHIDES OF GROUP VIII 319 

behavior is characteristic of certain peroxides, as mangan- 
ese and lead dioxides. 

The Hydroxide, Ni(0H)3, is formed similarly to the 
cobalt compound. Nickel Tctroxide, NiO^, is said to exist 
also. 

The Sulphides of the iron subgroup as a rule correspond 
quite closely to the lower oxides, for example, CoS, NiS, 
and FeS. Sulphides higher than the disulphides, how- 
ever, are not known. 

Ferrous Sulphide is a black substance and is used for 
generating H2S. It is usually made for that purpose by 
fusing the metal and sulphur together. It may also be 
obtained by the addition of ammonium sulphide to a 
ferrous salt : — 

FeSO, + (NH4)2Sri^(NH4)2S04 + FeS. 

Iro7i Disitlphide, pyrites, fool's gold, FeS2, usually oc- 
curs as a lustrous or yellow-colored substance of variable 
crystalline forms, with a specific mineralogical name for 
each. Some of the crystals are almost perfect. It is 
chiefly used on account of the sulphur contained in it. 
Iron forms several other sulphides which occur in nature, 
as FcySg or Fe^^S^Q, known as pyrrhotite. This frequently 
contains copper and nickel and cobalt which give the ore 
value. The percentage of sulphur may be as high as that 
in some pyrites, which are burned to make sulphuric acid, 
but it does not answer for that purpose without auxiliary 
heat. The ratio of the iron and sulphur is the important 
factor. 

A few Selenides occur in nature, generally accompany- 
ing the sulphides. The Telhirides are generally rarer 
than the selenides. Both show analogy to the sulphides. 

A review of the oxides of the remaining members of 



320 GENERAL INORGANIC CHEMISTRY 

this group would be even more technical than those 
already considered. Attention may be directed to just 
one ; namely, Osmium Tetroxide, OSO4, often improperly 
called osmic acid. It is used to a certain extent in stain- 
ing tissue which is to be examined microscopically. It 
is easily decomposed to a lower black oxide by organic 
matter. 

EXERCISES 

1. Show the resemblance of magnetite to the spmel group of 
minerals. 

2. Compare the graphic formulas for the three-fourths oxides 
of the iron subgroup. 



CHAPTER L 
BINARY COMPOUNDS OF GROUPS IV AND V 

Carbides 

When carbon is heated with a metal, a carbide is formed. 
This also occurs in part when the oxide is heated with 
carbon when it is first reduced to the metal. The ease 
and extent of the formation depends upon the metal 
and temperature. In 1808, Davy described potassium 
carbide, the first carbide recorded. In 1862, Wohler 
made an impure calcium carbide by direct synthesis. Al- 
though it was known that the carbon in white iron existed 
there as a carbide, it required the use of the heat of the 
electric furnace to open the field of this unique class of 
substances to investigation. Moissan prepared the carbides 
of many metals by this means. 

Many carbides are decomposed by water, giving the 
oxide or hydroxide of the metal and a hydrocarbon. Some 
are attacked only by acids, others by alkaline hydroxide 
solutions, and still others are among the most resistant 
compounds known. The gaseous hydrocarbons given off 
by the action of water or acids upon the carbides are 
methane and acetylene in the main. Methane is produced 
from Al^Cg and acetylene from CaC2. Thorium and ura- 
nium carbides (ThC2 and U2C3) produce gaseous, liquid, 
and soHd hydrocarbons. One of the explanations offered 
(by Mendelejeff) to account for the existence of natural 
gas and oil, presupposes the existence of a variety of car- 
bides within the earth, which are decomposed to form a 

321 



322 GENERAL INORGANIC CHEMISTRY 

mixture of hydrocarbons when water comes in contact 
with the carbides. 

Some carbides, as those of iron, are dissolved in the 
sohd metal (solid solution) and give to it such pecuHar 
properties as one observes in some cast iron and steels. 
Of the number of carbides known, the following are at 
present the most important : — 

Calchtm Carbide, CaCg, first prepared commercially in 
1894, is made by fusing limestone and carbon (as coke, 
charcoal, or coal) together in an electric furnace : — 

CaO + 3 C = CaC^ + CO. 

It is a brilliantly lustrous crystalline sohd which de- 
composes in the presence of water with the evolution of 
acetylene : — 

CaC^ + 2 H2O - t C2H2 + Ca(0H)2. 

This is the reaction when the carbide is pure. However, 
the lime and coke are liable to contain phosphorus, sulphur, 
and silicon compounds, when phosphine, hydrogen sul- 
phide, and hydrogen sihcide are generated also. The 
main use of calcium carbide is for the generation of acety- 
lene, but it is also used in making cyanamide and in desic- 
cating liquids. 

Boi'on Carbide, BgC, is one of the most stable and hard- 
est known compounds. It is nearly as hard as the dia- 
mond ; in fact, the powdered crystals may be used to polish 
some diamonds. BC has also been prepared. 

Silicon Caj^bide, carborundum, SiC, is made by heating 
to about 2500°, by means of an electric current (process of 
Acheson), a mixture of quartz sand and coke, with a little 
salt. Large carbon electrodes are so placed that the cur- 
rent will follow a connecting core of carbon, which is sur- 
rounded by the mixture, and heat it. After the current 



BINARY COMPOUNDS OF GROUPS IV AND V 323 

has passed awhile, the core becomes surrounded by a mass 
of brilUant iridescent crystals of SiC. Carborundum 
ordinarily resists the action of chemicals, but it is decom- 
posed by alkalies. It is used to line the walls of puddling 
furnaces in making steel. It is very hard, owing to which 
property it is used extensively as an abrasive material. It 
is as hard as the ruby, but not so hard as the diamond. 
By partially removing the oxygen from Si02, Siloxicon, 
SiOC, is produced. SiC2 has also been prepared. 

Iron Carbide, cementite, FcgC, is made in the smelting 
of iron ore by the blast furnace. When cast iron or steel 
is dissolved in hydrochloric acid, hydrogen and methane 
are evolved. Perhaps other iron carbides exist, but none 
has been separated. Nearly pure iron is called ferrite. 
A mixture of that and the cementite is called pearlite. 
Micro-photographs of different irons show a variety of 
crystals, which are attributed to various mixtures to which 
the terms sorbite, martensite, and troostite are applied by 
the metallurgist. 

Nitrides 

The Nitrides, a few of which are known, are usually 
made by direct union of the element with nitrogen or by 
heating the element in an atmosphere of ammonia. If 
made by either method, the nitrogen appears to retain 
its trivalent character. P'or example, lithium combines 
with nitrogen at ordinary temperatures to form lithium 
nitride, LigN. When magnesium is heated in an atmos- 
phere of nitrogen, Mg3N2 is produced. This reaction is 
utilized in separating nitrogen from argon in the air. 
When calcium is burned in the air, Ca3N2 is produced 
along with the oxide. These reactions are facihtated by 
the presence of some substance which prevents the oxida- 



324 GENERAL INORGANIC CHEMISTRY 

tion of the metal. For example, if magnesium is heated 
in the presence of calcium carbide in an electric furnace, 
the nitrides Mg3N2 and Ca3N2 are formed. As a rule the 
nitrides are decomposed by water with the production of 
ammonia. Boron nitride was one of the earliest nitrides 
known. When heated with water in the form of steam, 
it is decomposed : — 

BN + 3 H3O = B(0H)3 + NH3. 

As a matter of fact, the ammonia neutralizes a part of 
the boric acid. The existence of boron nitride within the 
earth has been offered as an explanation for the presence 
of boric acid in the waters of some lakes, which usually 
contain some ammonia. 

If sodium or potassium is heated in an atmosphere of 
ammonia, one hydrogen atom is replaced by the alkali 
metal, and NaNHg, sodamide, or KNH2, potassamide, 
results. They are decomposed by water : — 

NaNH2 + H2O = NaOH + NH3. 

Many phosphides, arsenides, and antimonides are known. 
They are made by the direct union of the elements. As 
the last two partake of a metallic character, their com- 
pounds will be considered under the head of alloys. 

EXERCISES 

1. Suppose phosphine and hydrogen sulphide are evolved when 
impure calcium carbide is treated with water ; write the reactions. 

2. The specific gravity of acetylene (C2H2) is 0.9. What 
volume would be occupied, at + 20° and 750 mm., by the gas 
generated from 480 grams of calcium carbide, 95 per cent pure? 



CHAPTER LI 
COMPOUNDS OF CARBON AND NITROGEN 

Carbon and nitrogen do not unite at ordinary tempera- 
tures, but there is union when a discharge of electricity 
occurs between carbon poles in an atmosphere of nitrogen. 
They combine at high temperatures in the presence of 
alkalies with the formation of alkaline cyanides, as potas- 
sium cyanide, KCN. From this may be made mercuric 
cyanide, Hg(CN)2, which on heating yields a gas, cyanogen^ 
(CN)^: — 

Hg(CN)2 = Hg + (CNV 

It is a colorless gas, very poisonous, and easily condensed 
to a liquid. It is insoluble in water and burns with a 
purple flame. Its structure is probably N = C — C = N. 
It acts in a measure like a molecule of chlorine, for we 
have numerous compounds in which CN enters as if it 
were an element like chlorine. 

Hydrogen Cyanide, HCN, is a colorless liquid, b.-p. + 
26.5°. It is prepared by treating a cyanide with an acid: — 

KCN + H^SO,!^ KHSO4+ \ HCN. 

The gas in a very dilute state has the odor of bitter 
almonds. It is one of the most poisonous substances 
known, a breath of it being sufficient to produce death ; 
hence the utmost caution should be exercised in working 
with it. It is very soluble in water, the solution being 
called hydrocyanic or prussic acid. It is, however, a very 
weak acid, scarcely reddening blue litmus, while some of 
its salts are decomposed by the carbon dioxide and water 
of the atmosphere. It is found in nature in combination 

325 



326 GENERAL INORGANIC CHEMISTRY 

in amygdalin, which is a constituent of some leaves, and 
of the kernels of certain stone fruits and of bitter almonds. 

As we secure HCN similar to HCl, so we may obtain 
CNCl, cyanogen chloride. These compounds may be 
written graphically as follows : — 

N = C-C = N, H-C = N, C1-C = N. 

We have learned that — NH2 acts in the same way, so 
we may obtain HgN — C = N, which is known as cyanamide. 

Wherever we have the group — C = N, especially in 
compounds of carbon, and boil the compound with water 
and an alkali, there is decomposition with the liberation 
of ammonia : — 

R - C = N + H2O + KOHz:>R - COOK + NH3. 
R indicates any element or radical. The potassium forms 
a salt of an organic acid. This is a very important reaction, 
as one may learn who studies the compounds of carbon. 
Recently it has assumed much practical importance, for it 
has been learned that when nitrogen is brought into con- 
tact with molten calcium carbide, a compound known as 
calcium cyanamide, CaCN2, is formed. This on being 
treated with water decomposes : — 

CaCN2 + H2O = Ca(0H)2 + H2CN2. 
And as the cyanamide is produced in the presence of an 
alkaline hydroxide, it is decomposed with the liberation of 
ammonia, hence the substance may be used in fertilizers. 
These reactions may solve in part the difficult problem of 
fixing nitrogen from the air and rendering it immediately 
available as plant food. 

A number of cyanides are derived from prussic acid, 
many of them being quite stable and useful. 

Potassium Cyanide, KCN, is obtained by heating potas- 
sium ferrocyanide [K^Fe(CN)Q] with an alkaline metal 



COMPOUNDS OF CARBON AND NITROGEN 327 

to decomposition and dissolving the cyanide formed in 
water : — 

K^FeCCN)^ + 2 K = 6 KCN + Fe. 

On evaporating the solution, the cyanide is obtained as a 
white solid which is easily decomposed by acids. It can 
be fused without decomposing. The fused salt has a 
strong affinity for oxygen, hence it is a strong reducing 
agent. This is shown when an easily reduced metallic oxide, 
like PbO, is stirred into the fused KCN. The molten 
metal collects in the bottom of the vessel, usually an iron 
crucible, and potassimn cya?tate floats above : — 

PbO + KCN = Pb + KCNO. 

The potassium salt on treatment with an acid is con- 
verted into cyanic acid, the formula for which may be 
written graphically in two ways, namely : — 

H-0-C = NandH-N = C = 0. 

In the latter arrangement we have the formula for iso- 
cyanic acid. If a water solution of the ammonium salt 
of this acid, ammonium isocyanate, NH^NCO, is evapo- 
rated to secure crystallization, crystals are obtained, to be 
sure, but not of that compound. The substance contains 
the same elements in the same proportions, and has the 
same molecular weight, CON2H4, but it is known as urea, 
and may be written graphically as follows : — 



= C 



AT — H 



\t— H 



328 GENERAL INORGANIC CHEMISTRY 

This substance occurs in the urine. Up to 1826 it was 
thought that a special "vital force" brought about the 
changes observed in compounds in living things, animal 
and vegetable. As the cyanates may be made directly 
from the inert elements and by simple treatment may be 
converted into a product of an animal, it became apparent 
that the same general laws govern chemical changes 
whether they occur in living or dead matter. This most 
important generalization was made by Wohler, who learned 
this method for preparing urea in the year referred to. 

The oxygen in the cyanates may be replaced by sulphur, 
when a thiocyanate results, as potassium thiocyanate, 
KCNS, for example. This substance in a water solution 
gives a red color with ferric, but not with ferrous, salts. 
It is one of the most delicate reactions known. 

Many important compounds are prepared from the 
cyanates and thiocyanates, which are fully considered in 
organic chemistry. 

Some of the metallic cyanides are insoluble in water; 
for example, when a solution of potassium cyanide is 
added to a silver nitrate solution, a precipitate of silver 
cyanide is obtained : — 

KCN + AgNOg zt KNO3 + I AgCN. 

On the addition of another molecule of KCN, the silver 
cyanide dissolves, due to the formation of a double cyanide, 
AgCN, KCN. The same reaction occurs with gold. This 
conduct is of great commercial importance, as these solu- 
tions are used in silver and gold plating, and for the ex- 
traction of gold and silver from their ores. If an acid, as 
hydrochloric acid, is added to the solution, the double cy- 
anide is decomposed, free HCN is produced, and the silver 
cyanide is reprecipitated. 



COMPOUNDS OF CARBON AND NITROGEN 329 

If nickel, cobalt, and iron salts are used, one obtains 
Ni(CN)2, 2 KCN ; CoCCN)^, 4 KCN ; Fe(CN)2, 4 KCN, 
and Fe(CN)3, 3 KCN. One may write these formulas 
as follows: K2Ni(CN)4, K4Co(CN)6, K4Fe(CN)6, and 
K3Fe(CN)g. If an acid is added to these solutions, they 
are not decomposed with the liberation of HCN, as in 
the cases referred to above, but the potassium is replaced 
by hydrogen; for example, one obtains H4Fe(CN)g and 
H3Fe(CN)g. They are known respectively as hydrofer- 
rocyanic and hydroferricyanic acids, and give salts. The 
iron in these compounds does not respond to the tests 
which ordinarily show its presence. 

Potassium Ferrocymiide, yellow prussiate of potash, 
K4Fe(CN)g, is obtained by heating together nitrogenous 
organic matter, like blood, horn, and so forth, with potas- 
sium hydroxide or carbonate in the presence of iron. The 
mass is leached, as the ferrocyanide is soluble in four parts 
of water. When the liquid is evaporated, large yellow 
crystals form. When brought in contact with ferric chlo- 
ride, Prussian blue, an important pigment, is formed : — 

3 K4Fe(CN)6 + 4 FeClg = jFe'''4Fe''3(CNX8 + 1 2 KCl. 

It will be noted that the iron is written in an unusual 
way. That is due to the fact that Fe^ may be replaced as 
in any ordinary compound of iron, whereas the Fe3 exists 
in the masked condition referred to above. The former is 
trivalent and the latter divalent. 

Potassium Ferricyanide, red prussiate of potash, 
K3Fe(CN)g, is formed from the ferrocyanide by oxidation, 
usually by means of chlorine. It is very soluble in water. 
On bringing ferricyanide and ferrous salts together in solu- 
tion, a precipitate known as TurnbuU's blue is formed : — 

2 K3Fe(CN)g + 3 FeSO^ = 3 K^SO^ + jFe'^gFe^CCNX^. 



330 GENERAL INORGANIC CHEMISTRY 

In this case Fcg is replaceable and divalent, while Fe2 is 
masked and trivalent. 

EXERCISES 

1. Calculate the specific gravity of cyanogen. 

2. How many pounds of pure calcium cyanamide would be re- 
quired to produce 40 pounds of ammonia ? 



CHAPTER LII 
ALLOYS 

We have considered the compounds of metals with 
non-metals and compounds of non-metals with non-metals. 
We may now study the compounds, quasi-compounds, or 
mixtures, among the metals. These homogeneous sub- 
stances are called alloys. Some of them were undoubtedly 
known a long time before some of the metals were obtained 
in anything like a pure condition. For example, brass, an 
alloy of zinc and copper, was known before zinc. How- 
ever, it is only within the last quarter of a century that 
alloys have been studied systematically, and even now they 
are not thoroughly understood. What has become known 
is based upon the application of principles of recent enun- 
ciation, the PJiase Rule, first laid down by Willard Gibbs 
in 1874. This important generalization, which is used by 
the most progressive investigators in physical chemistry, 
is too complicated for explanation in an elementary text. 
Some of the simplest difficulties encountered, however, will 
be hinted at. 

Copper and zinc are soft metals and have characteristic 
colors. When alloyed, they form brass, which is hard in 
comparison and has a color which is not intermediate be- 
tween the two. Copper alloyed with antimony (Cu2Sb) 
has a violet color (" Regulus of Venus"). Lead melts at 
H- 327°, tin at -f 232°, and bismuth at -h 270°. An alloy 
of the three in the proportion 1:1:2 does not melt at the 

331 



332 GENERAL INORGANIC CHEMISTRY 

average temperature + 275°, but melts at + 95°. If the 
electric conductivity of silver is placed at 100, then the con- 
ductivity of gold is 80 by the same standard. The conduc- 
tivity of an alloy of the two is not the average 90, but 15. 
The specific gravity of lead is 11.4 and tin 7.3. An alloy 
with 40 per cent, of tin has a specific gravity of 9.5. The 
calculated value for the mixture is 8.9. Platinum is insolu- 
ble in hydrochloric acid, but when present in some alloys 
it is soluble. As a rule, alloys are harder, hence more 
elastic and sonorous, than the constituent metals. The 
melting point is lower, the conductivity less, the specific 
gravity greater, and the chemical conduct different, which 
facts indicate that alloys are not mixtures, but chemical 
compounds. But chemical compounds require that the 
elements entering in them be in atomic ratio. This is not 
the case, for we may secure alloys of two metals in many 
different proportions. There are cases, however, where 
we may obtain definite crystalline compounds in which the 
metals are in strict atomic proportions, as for example, 
SnMg2, SbCug, SbCug, and SnCug. These substances are 
distinct bodies, characterized by properties quite distinct 
from the constituents of which they are composed. In 
other cases there is an indication of the formation of com- 
pounds, but they are comparatively unstable and have not 
been isolated in a pure state. In still other cases the 
metals form no compounds whatever with each other, but 
dissolve to different extents in one another. In some 
cases, metals show only the slightest indication of union 
with or solution in each other. 

Alloys are usually made by melting a definite amount of 
the metal with the highest melting point, with precautions 
to prevent oxidation, and adding the proper amount of the 
second metal in small pieces a little at a time and stirring 



ALLOYS 333 

the mixture. The material becomes homogeneous ; that is, 
one metal is dissolved in the other. When cooled the mass 
soHdifies, freezes, and retains its homogeneity in a measure. 
We thus have a solid soliUio7t. 

We have learned that " a solution is a chemically and 
physically homogeneous mixture, of which the composi- 
tion, within certain limits, can undergo continuous varia- 
tion ; the limiting compositions within which the mixture 
remains homogeneous are the limits of existence of the 
solution." That is to say, water will dissolve from o to 
26.4 per cent of its weight of sodium chloride at + 18°, 
but not more, and be a homogeneous liquid. In the same 
way, solid aluminum will hold in solution from o to 50 per 
cent of zinc at + 380°, but no more. 

The freezing point of water is lowered when salt is dis- 
solved in it and in the proportion added. So when the 
metal X is added to F, the fusing point of Y is lowered 
and in proportion to the amount of X added. Also, when 
a little of Y is added to X, the fusing point of X is low- 
ered in the same manner, the extent being dependent upon 
the amount of Y added. If fusing point curves are con- 
structed for the two cases, there will be a point where they 
intersect. A fused mixture of the two metals in the pro- 
portions indicated at that point will solidify as a uniform 
mass, a solid solution, or eutectic. 

Usually a liquid solvent dissolves more of a solid solute 
at a high temperature than it does at a lower one. When 
the solution is cooled, the excess of the solute separates 
out as a solid, ordinarily crystalline. This is true also of 
solutions of liquid mixtures in each other. If the fused 
mixture has the metals present in any other proportion 
than that constituting an eutectic, and is allowed to so- 
lidify, the excess of the solvent, which is the metal in 



334 GENERAL INORGANIC CHEMISTRY 

larger proportion, will separate in the pure condition. If 
the metals unite to form compounds, such as referred to, 
then the matter involves a compound and its solubility in 
the pure metal in excess, or the reverse. When there are 
several metals, they may form compounds among them- 
selves, and each has a different solubility. As we cool the 
liquid, we have some of each metal or compound separating, 
as when we cool a water solution of mixed salts. The size 
of the crystals of each in the latter case depends in a 
measure upon the rate of cooling. This is also true for 
alloys, but the alloy is usually completely solidified, conse- 
quently we have a mixture, that is, a solid solution of 
metals and alloys in the metal. If a solidified alloy is 
polished and etched, the microscope will reveal the pres- 
ence of the metallic compounds, the eutectic, and the pure 
metal in excess. The properties of the alloy are very de- 
pendent upon the rate of chilling. 

A number of alloys has been prepared. Many of them are 
of tremendous commercial importance. Only a few of the 
various groups will be mentioned here, as attention was di- 
rected to others when the individual metals were considered. 

Group I. An alloy of sodium with lO to 30 per cent 
of potassium melts at zero, and remains liquid through a 
wide range of temperatures. It has been used for filling 
thermometers. 

Copper forms a number of alloys. Brass is an alloy of 
copper and zinc, to which tin and lead are often added. 
Brass is hard, may be cast, and is easily worked with 
tools. Copper and tin form alloys known as bronze, gun 
metal (of which cannon were formerly made), and bell 
metal (with about 22 per cent of tin). With 33 per cent 
of tin, speculum metal is produced. It takes a high 
polish and is used in optical instruments. Copper, tin, 



ALLOYS 335 

and a small amount of manganese give manganese bronze, 
of which propellers for ocean steamships are made. It 
is strong and is little affected by salt water. Phosphor- 
bronze contains phosphorus instead of manganese. It is 
quite strong. 

The *' nickel" coin of the United States contains 75 per 
cent of copper and 25 per cent of nickel. German silver 
contains 60 per cent of copper, 20 per cent of zinc, and 
20 per cent of nickel. 

Copper with less than 10 per cent of aluminum gives 
an alloy possessing considerable strength and resembling 
gold in color. 

Silver and gold are alloyed together, or more usually 
with copper, for useful purposes. The silver coins of the 
United States contain 10 per cent copper and are known 
as 900 fine, 1000 being pure silver. Gold coins contain 
90 per cent gold, the remainder being copper or silver or 
both. Gold used for jewelry contains a larger proportion 
of copper or silver. Usually jewelry is made of from 12 
to 16 carat gold. The difference in color noted in gold 
coins and jewelry is due to the different proportions of 
gold, silver, and copper. 

Group II. Mercury dissolves many of the metals at 
ordinary temperatures. These alloys are called amalgams. 
Crystalhne compounds may be separated in many cases. 
When sodium is placed in mercury, it dissolves with the 
production of much heat. On coohng, after sufficient 
sodium has been added, the sodium amalgam solidifies. 
Reference has already been made to it as well as to 
ammonium, silver, and gold amalgams. Tin amalgams 
were once used for "silvering" mirrors. Silver and tin 
amalgams, when first prepared, are soft, but quickly 
harden, hence they are used in dentistry. 



336 GENERAL INORGANIC CHEMISTRY 

Group III. Aluminum and titanium form an alloy almost 
as light as the former metal and very strong. 

Groups IV and V. Tin and lead in the proportion of 4 : i 
form pewter ; and i : i to produce common solder. If the 
proportion of tin is greater, it is known as '' fine solder " ; 
whereas if the lead is in greater amount, it is ** common 
solder." Lead alloys with arsenic and antimony have been 
referred to. "Fusible metals" are alloys of lead, tin, and 
bismuth, and often cadmium. " Wood's metal," containing 
4 parts of bismuth, 2 of lead, i of tin, and i of cadmium, 
melts at + 60.5°. Cerium alloyed with 70 per cent iron 
gives off brilliant sparks when scratched with a piece of 
steel. 

Groups VI, VII, and VIII. Alloys of the metals in these 
groups are of immense commercial importance. Chrome, 
molybdenum, tungsten (and vanadium), and manganese 
steels have recently acquired noteworthy prominence, as 
mentioned. Ordinary iron and steel contain carbides and 
silicides, which form solid solutions with pure iron. 

The platinum metals usually occur alloyed together in 
nature. Platinum-iridium alloys are harder and more re- 
sistant to the action of chemicals than either metal alone. 
The international metrical standards are made of platinum 
with 10 per cent iridium. 



INDEX 



Acids are all listed under " acid " and " acids," and salts under the positive radi- 
cal. The names of persons are followed, when important, by the dates of birth and 
death. 



Abel, Sir F. A. (1827-1902), 87. 
Acetylene, 321, 322. 

AcHESON,E. G. (1 856-- ), 88, 322. 

Acid, antimonic, 280. 

arsenic, 278. 

arsenious, 278. 

boracic, 129, 235. 

boric, 129, 235, 307. 

bromic, 308. 

carbonic, 99, 241. 

"chamber," 287. 

chloric, 306, 307, 309. 

chlorous, 308. 

chromic, 299. 

cobaltic, 318. 

cyanic, 327. 

dithionic, 289. 

ferric, 317. 

formic, 100. 

hydrazoic, 187. 

hydriodic, 63. 

hydrobromic, 62. 

hydrochloric, 51, 60, 244. 

hydrochlor-platinic, 204. 

hydrocyanic, 325. 

hydroferricyanic, 329. 

hydroferrocyanic, 329. 

hydrofluoric, 63. 

hydrofluosilicic, 200. 

hydronitric, 187. 

hypobromous, 306. 

hypochlorous, 304. 

hyponitrous, 264. 



hypophosphorous, 277. 
hyposulphurous, 283, 288. 
iodic, 308. 
isocyanic, 327. 
manganic, 31 1. 
marine, 60. 

meta-aluminic, 239, 311. 
metabismuthic, 280. 
metaboric, 236, 
metamanganous, 311. 
metantimonic, 280. 
metaphosphoric, 275. 
metaplumbic, 262. 
metarsenic, 278. 
metasilicic, 253, 255. 
metastannic, 200, 261. 
metatitanic, 259. 
metavanadic, 281. 
molybdic, 300. 
muriatic, 60. 
"niter," 286. 
nitric, 72, 264, 266, 267, 268. 

action of, 269. 

fuming, 269. 

properties of, 268. 
nitrosyl-sulphuric, 285. 
nitrous, 265, 266. 
orthoantimonic, 280. 
orthoantimonious, 279. 
, orthoarsenic, 278. 
orthoboric, 235. 
orthocolumbic, 281. 



337 



338 



INDEX 



Acid, orthophosphoric, 202, 275. 
orthosilicic, 253, 255. 
orthotantalic, 281. 
ortho-thiocarbonic, 251. 
orthovanadic, 281. 
osmic, 320. 
oxalic, 308. 
percarbonic, 245. 
perchloric, 309. 
periodic, 309. 
permanganic, 312. 
persulphuric, 288. 
phosphorous, 202, 274. 
poly-metastannic, 261. 
poly-metatitanic, 259. 
prussic, 325. 
pyroantimonic, 280. 
pyroantimonious, 279. 
pyroarsenic, 278. 
pyrophosphoric, 275. 
selenic, 296, 
selenious, 296. 
silicic, 253. 
sulphuric, 1 14, 284. 

chamber process, 285. 

contact process, 284. 

fuming, 288. 

Nordhausen, 288. 

occurrence in the air, 84. 

properties, 287. 
sulphurous, 283. 
telluric, 297. 
tellurous, 296. 
tetraboric, 236. 
thiocarbonic, 251. 
thiosulphuric, 288. 
trisilicic, 256. 
trithionic, 289. 
tungstic, 301. 
uranic, 301. 
"Acide carbonique," 97, 
Acidimetry, 71. 
Acids, 64. 
arsenic, 278. 



definition of, 69. 

halogen, 60, 65. 

polytungstic, 301. 

thionic, 289. 
Actinic rays, 126. 
Actinium, 167. 
"Active oxygen," 32. 
"Aer vitriolicus," 29. 
Affinity, chemical, 6, 104. 
"After damp," 92. 
Agate, 136, 252'. 
Air, 78. 

composition, 78. 

impurities in, 84. 

liquid, 79. 
Alabaster, 291. 
Albite, 66. 

Albuminoid substances, 1 13. 
Alg?e, 43, 113. 
Alkali act, 242. 

industry, 242. 

metals, 66. 

preparation, 67. 
properties, 68. 
Alkalies, 69. 
Alkalimetry, 71. 
"Alkaline air," 74. 
Alkaline earth elements, 125. 
Alkol, 122. 
Allotropism, ^^. 
Alloy steels, 336. 
Alloys, 331. 
Alluvial soils, 258. 
Alpha-particles, 166. 
Alum, dissociation of, 42. 
Alumina, 131, 236. 
Aluminates, 239. 
Alumino-thermic process, 13] 
Aluminum, 18, 130, 135. 

alloys, 335, 336. 

bronze, 132. 

carbide, 321. 

carbonate, 249. 

chloride, 198. 



INDEX 



339 



hydroxide, 237. 

oxide, 236. 

phosphate, 277. 

silicate, 257. 

sodium tluoride, 56. 

sulphate, 293. 

sulphide, 239. 
Alums, 293. 
Aluiidum, 237, 
AiBalgams, 146, 335. 
Amethyst, 252. 
Ammonia, 74, 76. 

hydrate, 223. 

-soda process, 243. 
Ammoniates, 76. 
Ammonium, 186. 

alum, 293. 

amalgam, 1S6. 

carbonate, 245. 

chloride, 193. 

dissociation of, 194. 

hydrate, 223. 

hydrogen carbonate, 243. 

hydroxide, 77, 223. 

isocyanate, 327. 

nitrate, 264. 

polysulphide, 224. 

sulphide, 224. 
Amorphous substances, 48. 
Ampere, A. M. (i 776-1836), 58. 
Amygdalin, 326. 
Analysis, 9. 

qualitative, 218. 
Andrews, Thomas (1813-1885), 75. 
Anhydrite, 292. 
Animal charcoal, 88. 
Anions, 212. 
"Annealing," 174. 
Anode, 212. 
Anthracite, 88. 
" Anti-chlor," 306. 
Antimonides, 324. 
Antimonuretted hydrogen, 189. 
Antimony, 18, 122. 



alloys of, 123. 

butter of, 202. 

hydride, 189. 

pentachloride, 202. 

pentoxide, 280. 

sulphides, 280. 

tetroxide, 280. 

trichloride, 201. 

trioxide, 279. 
Apatite, 118, 276. 
Aqua fortis, 268. 

regia, 270. 
Aqueous vapor, 83. 
Aragonite, 247. 

Arfvedson, J. A. (1792-1841), 66, 68. 
Argentan, 145. 
Argentic compounds, 149. 
Argentite, 150. 
Argentous compounds, 149. 

oxide, 226. 
Argentum, 18. 

vivum, 146. 
Argon, 18, 78, 80, 323. 
Argyrodite, 138, 150. 
Aristotle (384-322 B.C.), 139. 

Arrhenius, Svante (1859 ), 

209, 213. 
Arsenic, 18, 120. 

flour, 121. 

glass, 277. 

hydrides, 188. 
modifications of, 1 21. 

pentoxide, 278. 
" porcelain," 277. 

sulphides, 279. 
trichloride, 201. 
trioxide, 121, 277, 
Arsenides, 324. 
Arsenious oxychloride, 202. 
Arsenites, 278. 
Arsenopyrite, 121. 
Arsenuretted hydrogen, 188. 
Arsine, 188. 
Asbestos, 126. 



340 



INDEX 



Asphalt, 89. 
Astronomy, i. 
Atmosphere, 78. 
Atom, II. 
Atomic theory, 12. 

weight, definition of, 12. 

weights, 18, 19, 106. 
table of, 18. 
Auric compounds, 149. 

halides, 195. 

hydroxide, 227. 

oxide, 227. 
Auri-pigment, 279. 
Aurous compounds, 149. 

halides, 195. 

oxide, 227. 
Aurum, 18. 
AVERAMl, 87. 

AVOGADRO, AmADEO (1776-1856), 37, 
44, 52. 

Avogadro's hypothesis, 37, 44, 52. 
Azoimide, 187. 
Azote, 72. 
Azurite, 149, 245. 

Bacillus nitrificans, I'jY. 
Bacon, Roger (i 214-1294), 16. 
Bacteria, 113. 

pathogenic, 40. 
Balard, a. J. (1802-1876), 58. 
Barite, 113. 
Barium, 18, 127. 

carbonate, 248. 

dioxide, 231. 

hydrosulphide, 232. 

hydroxide, 231. 

nitrate, 272. 

oxide, 231. 

perchlorate, 309. 

sulphate, 292. 

sulphide, 232. 
Barometers, 147. 
Baryta, 231. 
" Barytes," 292. 



Bases, 69, 77. 

Basic Bessemer process, 175. 

carbonates, 249. 

Open-hearth process, 175. 
"Batch," 254. 

Baumann, Eugen (1846-1896), 55. 
Bauxite, 130, 237. 
Bayen, Pierre (1725-1798), 78, 
Becher, J. J. (1635-1682), 78. 
Becquerel, a. H. (1852-1908)5 

163. 
Bell metal, 334. 
Bemont, Gustave, 128. 
Bengal saltpeter, 271. 
Benzene, 89. 

Bergmann, T. O. ( 1 735-1 784), 161. 
Berthollet, C. L, ( 1 748-1 822), 74. 
Beryl, 126. 
Beryllium, 18, 126. 
Berzelius, J. J. (1779-1848), 66, 116, 

136, 137, 138, 157, 158. 
Bessemer process, 174. 
Beta-particles, 166. 
"Bichloride," 197. 
Biology, I. 
"Biscuit firing," 257. 
Bismuth, 18, 123. 

basic carbonates, 250. 

butter of, 202. 

compounds, 280. 

oxides, 280. 

oxychloride, 202 

oxynitrate, 272. 
. subnitrate, 272. 

sulphides, 281. 

trichloride, 201. 
Bismuthyl nitrate, 272. 
Bituminous coal, 88. 
Black, Joseph (i 728-1 799), 97, 126, 

128. 
Black band ore, 170. 

lead, 88. 
" Blacksmith scales," 317. 
Blast furnace, 171. 



INDEX 



341 



Bleaching, 254, 304. 

powder, 244, 305. 
Blende, 234. 
Bloodstone, 252. 
" Bloom," 277. 
" Blooms," 174. 
Blowpipe, 95. 
Blue copper, 227. 

glass, 317. 

-stone, 291. 

vitriol, 291. 
Bog iron ore, 316. 
Boiler scale, 40. 

Boisbaudkan,Lecoqde(i838 ~ 

134, 181. 
Bolton, Wp:kner von, 157. 
Boracite, 129, 236. 
Borax, 129, 235, 236. 
Bordeaux mixture, 291. 
Borides, 130. 
Bornite, 149. 
Boron, 18, 129, 135. 

anhydride, 235. 

carbides, 322. 

chloride, 198. 

fluoride, 198. 

hydroxide, 235. 

nitride, 130, 324. 

trichloride, 198. 

trifluoride, 198. 

trioxide, 235. 
Bort, 86. 
Boyle, Robert (1627-1691), 75. 

Brand ( 1695), 118. 

Brandt, Georg (1694- 1768), 176. 
Brass, 145, 331, 334. 
Brauner, Bohuslav, 117. 
Braunite, 161, 311. 
Bridge-elements, ill. 
Brimstone, 113. 
Bromates, 308. 
Bromine, 18, 55, 58. 

compounds containing oxygen, 56. 

solid, 55. 



Bronze, 138, 334. 

Brown hematite, 170, 316. 

Bruyn, Lobry de (1857-1904), 186. 

BuNSEN, R. W. von (1811-1899), 

68. 
Bunsen burner, 95. 

Cadmia, 145. 
Cadmium, 18, 145. 

hydroxide, 233. 

oxide, 233. 

sulphide, 234. 
Cadmous hydroxide, 233. 

oxide, 233. 
Caesium, 18, 67. 

oxides, 223. 
Calamine, 144, 248. 
Calcite, 247. 
Calcium, 18, 127. 

carbide, 321, 322. 

carbonate, 247. 

chlorate, 306. 

chloride, 197. ■ 

cyanamide, 326. 

dioxide, 231. 

fluoride, 56, 196. 

hydride, 127. 

hydroxide, 230. 

inetasilicate, 119. 

nitrate, 272. 

nitride, 127, 323. 

oxide, 127, 230. 

phosphate, 118, 276. 

sulphate, 291. 

sulphide, 232. 

thiocarbonate, 251. 
Calcothar, 316. 
" Caliche," 270. 
Calomel, 197. 
Carat, 86, 155. 
Carbides, 89, 321. 
Carbon, 18, 86. 

amorphous, 88. 

compounds with nitrogen, 324. 



342 



INDEX 



Carbon dioxide, 90, 97. 

occurrence in the air, 82. 
properties, 98. 

disulphide, 90, 250. 

hydrides, 91. 

monoxide, 90, 100. 

occurrence of, 89. 

oxides, 97. 

oxy-sulphide, 251. 

suboxide, 102. 

sulphides, 250. 

tetrachloride, 199. 
Carbonates, 97, 241. 

acid, 241. 
Carborundum, 137, 322. 
Carboxy-hemoglobin, loi. 
Carburetting, 94. 
Carnallite, 67, 193. 
Carnotite, 164. 
Cassiterite, 138, 260. 
Castner, H. Y. (1859-1899), 131. 
Castner process, 222, 243. 
Catalysis, 55. 
Cathode, 212. 
Cations, 212. 
Caustic potash, 223. 

soda, 222. 
Cavendish, Henry (1731-1810), 

26. 
Celestite, 127. 
Cell, Leclanche, 312. 
Cementite, 323. 
Ceria, 259. 
Cerite, 137. 
Cerium, 18, 137. 

alloy with iron, 137, 336. 

oxide, 259. 
Cerussite, 141, 249. 
Chalcedony, 252. 
Chalcocite, 149. 
Chalcopyrite, 149, 227. 
Chalk, 248. 

Chalybeate waters, 250. 
"Chamber crystals," 285. 



Chaptal, J. A. ( 1 756-1832), 72. 
Charcoal, 88. 

properties, 89. 
Chemical affinity, 6, 104. 

changes, 6. 

energy, 6. 

equation, 25. 

formula, 24. 

properties, 27. 

reaction, 24. 
Chemism, 6. 
Chemistry, i, 2. 
Chili saltpeter, 270. 
"Chilled" shot, 122. 
Chlorates, 306. 
" Chlorinated soda," 304. 
Chlorine, 18, 51. 

bleaching action, 56, 304. 

heptoxide, 309. 

monoxide, 303. 

oxides, 303. 

preparation, 53. 

tetroxide, 307. 

trioxide, 308. 
Chlorophyl, 98. 
Chlor-platinates, 204. 
Chromates, 299. 
Chrome-alum, 293. 

-iron stone, 159. 

-potassium alum, 293. 

yellow, 272, 300. 
Chromic hydroxide, 298. 

oxide, 297. 
Chromite, 298. 
Chromium, 18, 159. 

monoxide, 297. 

normal salts, 298. 

"passive," 160. 

sesquioxide, 297. 

sulphides, 300. 

trioxide, 298. 
Chromous oxide, 297. 
Chrysoberyl, 239. 
Cinnabar, 146, 234. 



INDEX 



343 



Claus, C. E. (1796-1864), 182. 

Clay, 130, 257. 

Cleve, p. T. (1840- 1 905), 135. 

Cleveite, 81. 

Coal, 88. 

gas, 95. 
Cobalt, 18, 170. 

chloride, 203. 

plating, 177. 

sulphide, 319. 

ultramarine, 318. 
Cobaltic hydroxide, 318. 

oxide, 318. 
Cobaltite, 170. 
Cobaltous-cobaltic oxide, 318. 

hydroxide, 318. 

oxide, 318. 

salts, 318. 
Coke, 88. 

Colemanite, 129, 236. 
Colloid, 238. 
Colloidal solutions, 155. 
Columbium, 18, 158. 

pentoxide, 281. 
Combining power, quality of, 104. 

quantity of, 105. 
Combustion, 31, 92. 
Common salt, 66, 192. 

solder, 336. 
Composition, qualitative and quanti- 
tative, 35. 
Compound, 9. 
Compounds, naming of, 24. 

saturated, 103. 

unsaturated, 103. 
Conductors, 211, 
" Converter," 175. 
Copper, 18, 149. 

alloys, 334. 

arsenite, 278. 

carbonates, 245. 

"coarse," 152. 

ferrocyanide, 207. 

glance, 227. 



sulphate, 291. 

sulphides, 227. 
Copperas, 294, 316. 
Coral, 247. 
Corpuscles, 12. 
Corrosive sublimate, 197. 
Corundum, 130,286. 
CouRTOis, Bernard (i 777-1 838), 55, 

58. 
Crawford, Adair (1748-1795), 128. 
Crocoisite, 141, 159. 
Cronstedt, a. F. (i 722-1 765), 176. 

Crookes, Sir William (1832 ), 

12, 87, 134. 
Cryolite, 56, 66, 130. 
Crystal forms, 46. 
Crystallization, 46. 

fractional, 164. 

water of, 47. 
Crystalloids, 238. 
Cubic niter, 270. 

CuLLEN, William (1710-1790), 75. 
Cullinan diamond, 86. 
Cupellation, 153. 
Cupric chloride, 195. 

compounds, 149. 

hydroxide, 225. 

oxide, 225. 

salts, 225. 
Cuprite, 149, 224. 
Cuprous chloride, 195. 

compounds, 149. 

hydroxide, 225. 

oxide, 224. 
C2iprum, 18. 
Curie, Pierre (i 859-1906), 128, 

163. 
Curie, Mme. Sklodowska, 128, 
163. 

CuRTius, Theodor (1857 ), 187. 

Cyanamide, 322, 326. 
Cyanides, double, 327. 
Cyanogen, 325. 

chloride, 326. 



344 



INDEX 



D ALTON, John (i 766-1 844), 11, 97, 

99. 
Dalton's law of partial pressures, 99. 
Davy, Humphry (1778-1829), 25, 51, 
60, 66, 68, 93, 127, 128, 264, 
321. 
Demarcay, Eugen, 181, 
Denitrification, 41, 73, 74. 
" Dephlogisticated air," 29. 
Destructive distillation, 74. 
Developers, 195. 
" Devil's touchstone," 137. 
Devitrification, 254. 

Dewar, James (1842 ), 80, 81. 

Dialysis, 238. 

Dialyzed iron, 317. 

Diamide, 186. 

Diamond, 86. 

Diamonds, artificial and synthetic, 

87. 
Diaspore, 237. 
Dicarbonates, 241. 
Dichromates, 299. 
Dimorphous substances, 115. 
Dissociation, 42. 

electrolytic, 211. 

of compounds (by heat), 205. 
Distillation, 34. 

destructive, 74. 
Dobereiner's lamp, 26. 
Dolomite, 126, 247. 
Drummond light, 230. 
Duhamel du Monceau (i 700-1 781), 

68. 
Dutch metal, 155. 

process, 249. 
Dysprosium, 18. 

Earth, 129. 

" Eau de Javelle," 304. 

Effervescent drinks, 97. 

Efflorescence, 50. 

Eka-silicon, 138. 

Ekeberg, a. G. (1767-1813), 158. 



Electrolysis, 211. 
Electrolytes, 211. 
Electrolytic dissociation, theory of, 

213. 
Electrons, 12. 
Element, definition of, 15. 

requirements of, 17. 
Elements, atomic weights of, 19. 

chemical, 15. 

classification of, 104. 

earth, 129. 

electrochemical character of, 105. 

list of, 18. 

metallic, 105. 

names of, 17. 

negative, 105. 

non-metallic, 105. 

positive, 105. 

relative abundance of, 20. 

symbols of, 20. 
Elhujar, Jean, Jose, and Fausto de, 

161. 
Emanium, 167. 
Emerald green, 278. 
Emery, 130, 236. 
Endothermic actions, 7. 
Energy, conservation of, 6. 
Epsom salts, 291. 
Equations, 25. 
Equivalence, 71. 
Equivalent weight, 38. 
Erbium, 18, 134. 
Ethane, 92. 
Europium, 18, 181. 
Eutectic, 333. 
Euxenite, 132. 
Exothermic actions, 7. 
Extraction, 46. 

Faraday, Michael (i 791-1867), 75, 

98, 211. 
Feldspar, 66, 130, 136, 256. 
Ferric chloride, 204. 
compounds, 175. 



INDEX 



345 



hydroxide, 316. 

nitrate, 272. 

oxide, 315, 316. 

sulphate, 295. 
Ferrite, 323. 
Ferromanganese, 162. 
Ferrous carbonate, 250. 

chloride, 204. 

chromite, 159. 

compounds, 175. 

-ferric oxide, 317. 

hydroxide, 316. 

oxide, 315. 

sulphate, 294. 

sulphide, 319. 
Ferrum, 18. 
Fertilizers, 276. 
Filters, 7. 
Filtrate, 7. 
Filtration, 7. 
" Fire air," 29. 
" Fire damp," 91. 
Fire extinguishers, 99. 
"Fixed air," 97. 
Fixer, 196. 
Flame, 93. 

luminous, 94. 
Fla^h-light powder, 127. 
Flint, 136, 252. 
Flores siilpJuiris, 113. 
Fluorine, occurrence, 56. 

preparation, 57. 

properties, 57. 
Fluorite, 196. 
Fluorspar, 56, 127, 196. 
Flux, 150. 
" Fool's gold," 319. 
P^ormula, chemical, 24. 
Fractional crystallization, 164. 
Franklinite, 144, 317. 
Freezing-points, depression of, 209. 
Furnace, " hailing," 242. 

blast, 171. 
" Fusible metals," 336. 



Gadolin, Johan ( 1 760-1852), 135. 
Gadolinite, 132. 

metals, 181. 
Gadolinium, 18, 181. 
Gakn, J. G. (1745-1818), 118, 161. 
Gahnite, 239. 
Galena, 113, 141, 262. 
Galilei, Galileo (1564-1642), 78. 
GalHum, 18, 133, 134. 
Galvanized iron, 145, 175. 
Gamma-rays, 166. 
Garnierite, 170. 
Gas, illuminating, 94. 
Gas carbon, 88. 

flame, 94. 

"sylvestre," 97. 
Gases, liquefaction of, 75. 

weight of a liter of, 62. 
Gastric juice, 60. 
Gautier,.I2I. 

Gay-Lussac, J. L.( 1 778-1850), 51, 66. 
Gay-Lussac tower, 286. 
Gay-Lussac's law, 51. 
Geber (Dschafar) (702-765), 16. 
Geology, i. 
German silver, 335. 
Germanium, 18, 138. 
Gersdorffite, 170. 
Gesner, Conrad von (15 16-1565), 

87. 
GiBBS, Willard (1839-1903), 331. 
Glass, 253. 

borax, 236. 

varieties of, 254. 
Glauber's salt, 290. 
Glover tower, 286. 
Glucinum, 18, 126. 
Gmelin, C. G., 67. 
Goethite, 316. 
Gold, 18, 150. 

alloys, 335. 

coins, 335. 

cyanide, 328. 

"fulminating," 227. 



346 



INDEX 



Gold hydroxide, 227, 

"leaf," 155. 

monoxide, 227. 

sulphide, 227. 

trioxide, 227. 
*' Golden fluid," 184, 
Goldschmidt alumino-thermic process, 

131- 
Granite, 252, 256. 
Graphite, 87. 
Green cinnabar, 318. 

fire, 272. 

vitriol, 294. 
Greenockite, 145, 234. 
Grotta del Cane, 97. 
GuERiCKE, Otto VON (1602- 1686), 79. 
Guignet's green, 298. 
Gun metal, 334. 
Gunpowder, 271. 

GuTTMANN, Oscar (1855 ), 271. 

Gypsum, 113, 127, 291. 

Hales, Stephen (i 677-1 761), 23. 
Halides, 191. 

Hall, C. ]VI. (1863 ), 131. 

Hall process, 237. 

Halogen acids, 60, 65. 

Halogens, 51, 58. 

Hampson, 80. 

Hatchett, Charles (i 765-1 847), 

i58._ 
Hausmannite, 161, 311. 
Hearth, 171. 
Heavy spar, 127, 292. 
Helium, 18, 81. 

Helmont, J. B. van (15 78-1 644), 97. 
Hematite, 170, 316. 

brown, 315. 
Hemoglobin, 10 1. 

Henry, William (1774-1836), 99. 
Heptane, 89. 

Hermann, Benedict, 148. 
Hexagonal system, 47. 
Hisinger, W. (1766-1852), 138. 



HiTTORF, J. W. (1824 ), 119. 

HjELM, P. J. (1746-1813), 161. 

HoFF, J. H. van't (1852- ), 208, 

212. 

Hofmann, F. (1660-1742), 128, 135. 

Holmium, 133. 

HooKE, Robert (i 635-1 702), 78. 

Horn silver, 150. 

Horsford's phosphates, 277. 

Hulett, G. a. (1868 ), 146. 

Humidity, 49. 
Hyacinth, 259. 
Hydrargillite, 237. 
Hydrargyrum, 18, 146. 
Hydrates, 48. 
Hydrazine, 186. 
Hydrides, 190. 
Hydrocarbons, 91, 321. 
Hydrogel, 238, 253. 
Hydrogen, 18, 22. 

antimonide, 189. 

arsenide, solid, 189. 

bromide, preparation, 62. 

chloride, chemical properties, 62. 
occurrence, 60. 
physical properties, 61. 
preparation, 51, 61. 

cyanide, 325. 

dioxide, 183. 

disulphide, 185. 

fluoride, 57, 63. 
preparation, 64. 
properties, 64. 

iodide, preparation, 63. 

monoxide, 183. 

occurrence, 27. 

peroxide, 183. 

phosphides, 188. 

preparation, 25. 

production, 27. 

properties, 23, 26. 

selenide, 186. 

silico-fluoride, 200. 

sulphide, 185. 



INDEX 



347 



telluride, 1 86. 

trinitride, 187. 
Hydrolysis, 42. 
"Hydrolyte," 127. 
Hydrone, 27, 68. 
Hydrosol, 238, 253. 
Hydrosulphides, 219. 
Hydroxides, 48, 216. 
Hydroxy!, 69. 
" Hypo-solution," 288. 
Hypobromites, 306. 
Hypochlorites, 304. 
Hyposulphites, 283. 
Hypothesis, II. 

atomic, 12. 

Avogadro's, 37, 44, 52. 

corpuscular, 13. ■ 

Ice, 99. 

machines, 75. 
Iceland spar, 247. 
Illuminating gas, 94. 
Indelible ink, 272. 
Indium, 18, 134. 
Introduction, I. 
Intumescence, 236. 
Iodine, 18, 55. 

pentoxide, 308. 

preparation, 55. 
Ionium, 167. 
Ionization, cause of, 214. 
Ions, 212. 
Iridium, 18, 179. 
Iron, 18, 170. 

carbide, 87, 323. 

cast, 172. 

disulphide, 319. 

metals, 169. 

"passive," 176. 

phosphates, 277. 

rust, 22, 317. 

sesquioxide, 316. 

"stains," 250. 

sulphide, 113. 



technical, 171. 

wrought, 173. 
Isometric system, 46. 
Israelites, 66. 

Jacinth, 259. 

Janssen, p. C. C. (1824 

Joule, J. P. (1818-1889), 6. 



),8i. 



Kahlenberg, Louis ( 1 870 ) , 238. 

Kainite, 291. 

Kalium, 18. 

Kaolinite, 257. 

" Kelp," 242. 

Kindling point, 93. 

KiRCHHOFF, G. L. ( 1 824-1 887), 68. 

Klaproth, M. H. (i 743-181 7), 138, 

161. 
"Kohl," 122. 
Krypton, 18, 81. 

" Labarraque's solution," 304. 

Labradorite, 66. 

Lac sulphuris, 115. 

" Lake dyes," 294. 

Lampblack, 88. 

Lamy, Claude (1820-1879), 134. 

Lanthanite, 249. 

Lanthanum, 18, 135. 

carbonate, 249. 

oxides, 239. 
Lapis infernalis, 272. 
" Laughing gas," 264. 
Lavoisier, A. L. (i 743-1 794), 8, 16, 

26, 29, 72, 78, 89, 97. 
Law, Avogadro's, 209. 

Boyle's, 208. 

Charles's, 208. 

Dalton's, 99. 

Gay-Lussac's, 208. 

Henry and Dalton's, 99. 

Mariotte's, 208. 

of the conservation of matter, 8. 

of the constancy of composition, 9. 



348 



INDEX 



Law of multiple proportions, 11, ( 

of octaves, 107. 

of partition, 46. 

periodic, 104, 107. 

Raoult's, 209. 

van't Hoff' s, 208. 

Arrhenius' statement of, 209. 
Lea, M. C. (1823-1897), 155. 
Lead, 18, 141. 

alloys, 143, 336. 

basic chromate, 300. 

carbonate, 249. 

-chamber process, 285. 

chloride, 200. 

chromate, 300. 

colic, 143. 

dioxide, 261. 

hydroxide, 142, 262. 

iodide, 201. 

molybdate, 301. 

monoxide, 261. 

nitrate, 272. 

oxides, 261. 

sesquioxide, 262. 

suboxide, 262. 

sulphate, 294. 

sulphide, 250, 262. 

tetrachloride, 201. 

tree, 141. 
Le Blanc soda process, 232, 242. 
Leguminosae, 73. 

Lenher, Victor (1873 ), i 

I-epidolite, 67. 

Lichens, 23. 

" Life air," 29. 

Lignite, 88. 

Lime, "air-slaked," 231. 

chloride of, 305. 

" fat," 230. 

" milk of," 230. 

"poor," 230. 

slaked, 230. 
Lime-light, 27, 230. 
Limestone, 89, 97, 127, 230, 247. 



" Lime-water," 230. 
Limonite, 170, 316. 

LiNDE, C. P. G. (1842 ), 8a 

Linnemann light, 259. 
Liquefaction of gases, 75. 
Litharge, 261. 
Lithia mica, 67. 

waters, 67. 
Lithium, 18, 66. 

carbonate, 245. 

nitride, 323. 

oxide, 221. 
Litmus, 23, 70. 

LoCKYER, Sir J. N. (1836 ), 81. 

"Lodestone," 317. 
Lollingite, 121. 
" Luminous paint," 232. 
Lunar caustic, 272. 
Lutecium, 18. 

Macquer, p. J. (171 8-1 784), 26. 
Magnalium, 132. 
Magnesia, 229. 

"alba," 247. 

" usta," 229. 
Magnesite, 89, 126, 247. 
Magnesium, 18, 126. 

carbonate, 247. 

chloride, 197. 

chromate, 300. 

hydroxide, 229. 

" milk of," 230. 

nitride, 127, 323. 

oxide, 127, 229. 

sulphate, 291. 
Magnetic oxide, 317. 
Magnetite, 170, 317. 
Malachite, 149, 245. 
Malacone, 81. 
Manganates, 312. 
Manganese, 18, 161. 

bronze, 335. 

carbonate, 250. 

chlorides, 310, 311. 



INDEX 



349 



dioxide, 53, 311. 

halides, 203. 

heptoxide, 312. 

monoxide, 310. 

oxides, 310. 

sesquioxide, 31 1. 

sulphides, 313. 

trioxide, 312. 
Manganic chloride, 311. 

hydroxide, 311. 

oxide, 311. 

sulphate, 311. 
Manganite, 161, 311. 
Manganites, 312. 
Manganous chloride, -310. 

hydroxide, 311. 

-manganic oxide, 311. 

nitrate, 310. 

sulphate, 310. 
Mantles, 259. 
Marble, 230, 247. 

Marggraf, a. S. ( 1 709-1 782), 68. 
Marignac, J. C. DE (181 7-1 894), 181. 
Marl, 248. 
" Marsh gas," 91. 
Martensite, 323. 
Marum, Martin van (i 750-1837), 

32, 75. 
Massicot, 261. 
Matches, 120. 
Matte, 152. 
Mayow, Johannes (i 645-1 679), 28, 

78. 
Meerschaum, 126. 
Membranes, 207. 
Menaccanite, 137, 259. 
Mendelejeff, D. I. ( 1 834-1 907), 

107, 138, 321. 
" Mephitic air," 72. 
Mercuric compounds, 147. 

cyanide, 325. 

oxide, 146, 233. 

sulphate, 292. 

sulphide, 234. 



Mercurous compounds, 147. 

oxide, 233. 

sulphate, 293. 

sulphide, 234. 
Mercury, 18, 146. 

chlorides, 197. 

iodides, 197. 

oxides, 233. 

sulphides, 234. 
Metallic hydrides, 190. 
Metals, 105. 
Metantimonites, 279. 
Metaphosphates, 275. 
Methane, 89, 91, 321. 
Methyl compounds, 92. 
Meyer, L. J. (1830-1895), 107. 
Mica, 66, 130, 136, 256. 
Microcosmic salt, 276. 
Mineral paint, 316. 

phosphates, 276. 
Minium, 261. 
Mirrors, 147. 
Mohr's salt, 316. 
MoissAN, Henri (1852-1907), 57, 58, 

87, 190, 321. 
Molecular weight, 35. 
Molecular weights, determination of, 

205. 
Molecule, the chemical, 15. 
Molybdenite, 301. 
Molybdenum, 18, 160. 

sulphide, 301. 

trioxide, 300. 
Monazite, 132, 137. 
Mond process, loi. 
Monoclinic system, 47. 
" Munox," 252. 
Mordant, 237. 

Morse, H. N. (1848 ), 208. 

Mortar, 230. 

Mosander, C. G. (1797-1858), 134, 
135- 

MULLER VON RJEICHENSTEIN, F. J. 

(1740-1825), 1X6. 



3 so 



INDEX 



MuRDOCK, William (1754-1839), 95. 

MUTHxMANN, WiLHELM, 1 37. 

Nascent condition, 56. 
Natrium, 18. 
Natrona, 66, 242. 

Natterer, J. A. (1821 ), 75, 

Natural gas, 89, 91. 
Neodymium, 18. 
Neon, 18, 81. 

Nernst, Walther (1864 ), 157. 

Nernst light, 259. 

Neutralization, 69. 

Newlands, J. A. R. (1 838-1 898), 106. 

Niccolite, 170. 

Nickel, 18, 170. 

carbonyl, 10 1. 

chloride, 203. 

coin, 335. 

hydroxide, 318. 

monoxide, 318. 

plating, 177. 

sesquioxide, 318. 

sulphide, 319. 

tetroxide, 319. 
Nickelic hydroxide, 319. 
NiLSON, L. Y. (1840-1899), 135. 
Niobium, 18, 158. 
Niter, 72, 271. 

cake, 290. 
Nitrates, 72, 268, 270. 

basic, 272. 
Nitric oxide, 264. 
Nitrides, 323. 
Nitrification, 41, 73. 
Nitrites, 265. 
" Nitro-aerial spirit," 29. 
Nitrogen, 18, 72, 118. 

dioxide, 264. 

fixation of, 326. 

iodide, 201. 

monoxide, 264. 

oxides, 263. 

pentoxide, 266. 



peroxide, 265. 

tetroxide, 265. 

trichloride, 201. 

trioxide, 265. . 
Nitrosyl chloride, 270. 
Nitrous oxide, 264. 
Noble, W. H. (1834-1892), 87. 
" Noble gases," 78, 80, 82. 
Nollet, Abbe (1700-1770), 207. 
Non-conductors, 211. 
Non-metals, 105. 

Norrls, J. F. (187 1 ), 117. 

Northmore, T. (1766-1851), 75. 

Octaves, law of, 107. 
Oil of vitriol, 284. 
Oligoclase, 66. 
Olivine, 87, 126, 256. 

Olszewski, K. S. (1846 ), 82. 

Onnes, K., 81, 82. 
"Open-hearth process," 174. 
Organic chemistry, 91. 
Orpiment, 121, 279. 
Orthoclase, 66. 
Orthophosphates, 275. 
Osmium, 18, 179. 

tetroxide, 320. 
Osmosis, 207, 
Oxidation, 31. 
Oxides, 31, 216. 

of the Negative Members of Group 
VII, 302. 

of Group VIII, 314. 
Oxone, 30, 222. 
Oxygen, 18, 29. 

chemical properties, 31. 

dihydride, 183. 

occurrence, 29. 

physical properties, 30. 

preparation, 30. 

uses, 31. 
Oxy-hemoglobin, loi. 
Oxyhydrogen lamp, 27. 
Ozone, 32, 57. 



INDEX 



351 



Palladium, 18, 178. 

" black," 179. 

halides, 204. 

"sponge," 179. 
Panning, 151. 
Paris green, 278. 
Parkes process, 153. 
Pasteur filter, 41. 
"Pay dirt," 151. 
" Pearl-ash," 245. 
Pearlite, 323. 
Peat, 88. 

Peligot, E. M. (1811-1890), 161. 
Pentlandite, 170. 
Perchlorates, 309. 
Periodates, 309. 
Periodic law, 104, 107. 
Permanganates, 313. 
Perovskite, 137, 259. 
Persulphates, 288. 
Petroleum, 89, 91. 
Pewter, 336. 

Pfp:ffer, W. F. (1845 ), 207. 

Phase rule, 331. 
" Philosopher's lamp," 26. 
"Philosopher's stone," 16. 
" rhlogisticated air," 72. 
Phosphate rock, 276. 
Phosphides, 324. 
Phosphine, 187. 
Phosphites, 275. 
Phosphor-bronze, 335. 
Phosphoric oxychluride, 202. 
Phosphorite, 276. 
Phosphorus, 18, 118. 

acids of, 274, 275. 

hydrides, 187. 

metallic, 1 1 9. 

oxides, 274. 

oxychloride, 202. 

pentachloride, 202. 

pentoxide, 275. 

red, 119. 

salt of, 276. 



sulphides, 277. 

trichloride, 201. 

trioxide, 274. 

yellow, 119, 
Phosphuretted hydrogen, 187. 
Photochemistry, 191, 195. 
Photography, 195. 
Physical changes, 2. 

properties, 26. 
Physics, I. 
"Pickling," 176. 
Pintsch gas, 95. 
Pitchblende, 164, 301. 
" Placer gold," 150. 
Plaster of Paris, 292. 
Platinum, 18, 180. 

"black," 180. 

chlorides, 204. 

-iridium alloy, 336. 

metals, 178. 
Plattnerite, 261. 
Pliny, Plinius Gaius Secundus (23- 

79 A.D.), 122, 138, 141. 
Plumbago, 88. 
Plumbum, 18. 

candidum, 138. 

nigrum, 141. 
" Pneumatic process," 174. 
Poison Valley-, 97. 
" Poisonous flour," 277. 
Pollucite, 67. 
Polonium, 167. 
Polychromates, 300. 
PolymolybdateSj 301. 
Poly-uranates, 301. 
Potash alkali, 245. 

red chromate of, 300. 

red prussiate of, 329. 

yellow prussiate of, 329. 
" Potashes," 244. 
Potassamide, 324. 
Potassium, 18, 66. 

alum, 293. 

aluminum sulphate, 293. 



352 



INDEX 



Potassium bromide, 193. 

carbide, 321. 

carbonate, 244. 

chlorate, 306. 

chloride, 193. 

chromate, 299. 

cobaltate, 318. 

cyanate, 327. 

cyanide, 325, 326. 

dichromate, 300. 

disulphate, 291. 

ferrate, 317. 

ferricyanide, 329. 

ferrocyanide, 326, 329. 

hydrate, 223. 

hydrosulphide, 224. 

hydroxide, 223. 

iodide, 193. 

manganate, 31 1. 

monoxide, 222. 

nitrate, 268, 271. 

occurrence, 66. 

oxides, 222. 

percarbonate, 245. 

permanganate, 312. 

-sodium alloy, 334. 

sulphate, 291. 
acid, 291. 

thiocyanate, 328. 

Potter, H. N. (1869 ),252. 

Praseodymium, 18. 
Precipitant, 7. 
Precipitate, 7. 

"per se," 233. 
" Precipitated chalk," 248. 
Pressure, critical, 75. 

osmotic, 207. 

partial, 44. 

solution, 44. 
Priestley, Joseph (1733- 1804), 29, 

60, 74. 
Propane, 92. 
Protyle, 12. 
Proustite, 150. 



Prussian blue, 329. 
Pyrargyrite, 150, 
Pyrite, 113. 
Pyrites, 170, 316, 319. 
Pyrolusite, 161, 311. 
Pyrophoric iron, 170. 
Pyrophosphates, 275. 
Pyrrhotite, 170, 319. . 

Quadratic system, 46. 
Qualitative composition, 35. 
Quantitative composition, 35. 
Quartation, 153. 
Quartz, 136, 252. 

fused, 253. 
Quick-lime, 230. 
Quicksilver, 146. 

Radicals, compound, 76. 
Radio-activity, 163. 
Radio-lead, 167. 
Radium, 16, 18, 127, 164. 

emanation, 166. 

Ramsay, Sir William (1852 ), 

78, 80, 81, 167. 
Rare-earths, 132. 
Rayleigh, J. W. Strutt, Lord 

(1842 ), 78, 80. 

Realgar, 121, 279. 
Red fire, 272. 

lead, 261. 

ocher, 316. 

precipitate, 233. 
Regular system, 46. 
" Regulus of Venus," 331. 
Reich, Ferdinand (i 799-1 882), 

134- 
Reversible reactions, 33, 54. 

Rey, Jean ( 1645), 29, 78. 

Rhodium, 18, 178. 
Rhodochroisite, 161, 230. 
Rhombic system, 47. 

Richards, T. W. (1868 ), 117. 

Richter, R. J. ( 1 823-1 869), 134. 



INDEX 



•353 



Rinmann's green, 318. 

Roasting, 121, 

Roberts-Austen, Sir W. C. (1843- 

1903), 206. 
Rock-crystal, 252. 
Rock salt, 66, 192. 
Roman alum, 293. 

RoscoE, Sir H. E. (1833 ), 158. 

Rubidium, 18, 67. 

dioxide, 223. 
Ruby, 130, 236. 
Ruddle, 316. 
Ruhmer lamp, 116. 
Ruthenium, 18, 178. 

trichloride, 204. 
Rutherford, Daniel (i 749-1 81 9), 
72, 78. 

Rutherford, Ernest (1871 ), 

166. 
Rutile, 137, 259. 

Safety lamp, 93. 

matches, 120. 
Sal ammoniacn7n, 193. 

mirabile, 290, 

soda, 242. 
Salt brines, 192. 

cake, 290. 

"harvesting,"' 192. 
Saltpeter, 72, 268, 271. 
Salts, 69. 

acid, 241. 

basic, 241. 

formation of, 217. 

normal, 241. 
Samarium, 18, 181. 
Samarskite, 132. 
Sand, 136, 252. 
Sapphire, 130, 236. 
Saturated compounds, 103. 
Scandium, 18, 133, 135. 
Scheeee, C. W. ( 1 742-1 786), 29, 51, 

53, 58, 118, 128, 161, 188. 
Scheele's green, 278. 



Scheelite, 160, 301. 
Schmidt, G. C, 163. 
Schonbein, C. F. ( 1 799-1868), 32. 
Schroder contact process, 284. 
Schrotter, 119. 

SCHWARZ, BeRTHOLD, 27I. 

Schweinfurt green, 278. 
Science, i. 

applied, I. 

duty of, 13. 

pure, I. 
Sciences, classification, I. 
Sea-water, 192. 

-weed, 55. 
Sefstrom, N. G. (1787-1845), 158. 
Selenates, 296. 
Selenides, 219, 319. 
Selenites, 296. 
Selenium, 18, 116. 

dioxide, 296. 

hydride, 186. 
Selenuretted hydrogen, 186. 
Semi-permeable partitions, 207, 
Shells, 248. 
Siderite, 97, 170, 250. 
Sidot's blende, 165. 
Siemens-Martin process, 174. 
Silex, 136. 
Silica, 136, 252. 
Silicates, 136, 253, 255. 
Silicides, 137. 
Silicon, 18, 136. 

carbide, 137, 322. 

dioxide, 252. 

hydrides, 190. 

hydroxide, 253. 

monoxide, 252. 

tetrachloride, 199. 

tetrafluoride, 199. 
Siloxicon, 323. 
Silt, 258. 
Silver, 18, 150. 

alloys, 335. 

allotropic forms, 155. 



354 



INDEX 



Silver carbonate, 246. 

chloride, 195. 

coins, 335. 

cyanide, 328. 

dioxide, 226. 

" fulminating," 227. 

glance, 227. 

halides, 195. 

nitrate, 272. 

normal carbonate, 246. 

oxide, 226, 

"oxidized," 155. 

-potassium cyanide, 328. 

suboxide, 226. 

sulphide, 227. 
" Silvering," 335. 
Slag, 150. 
Slaking, 230. 
Smalt, 318. 
Smaltite, 170. 
" Smelling salts," 75, 245. 
Smelting, 152. 

Smith, Alexander (1865 ), 115. 

Soapstone, 126. 
Soda, 242. 

ash, 244. 

cooking, 244. 

laundry, 242. 

washing, 244. 
Sodamide, 324. 
SoDDY, Frederic, 167. 
Sodium, 18, 66. 

alum, 293. 

aluminate, 239. 

amalgam, 335. 

bicarbonate, 243. 

borate, 66. 

carbonate, 66, 242. 

chloride, 51, 66, 192, 242. 

dicarbonate, 243, 244. 

dioxide, 222. 

fluoride, 66. 

hydrate, 222. 

hydrogen carbonate, 243, 244. 



hydrosulphide, 224. 

hydroxide, 222, 243. 

iodate, 308. 

manganate, 312. 

metastannate, 261. 

monoxide, 221. 

nitrate, 268, 270. 

occurrence, 66. 

oxides, 221. 

permanganate, 312. 

phosphate, 276. 

-potassium alloy, 334. 

silicate, 253. 

stannate, 261. 

sulphate, 66, 242, 290. 

sulphide, 223, 242. 
higher, 224. 

tetraborate, 236. 

thio-metastannate, 261. 

thiosulphate, 288. 

zincate, 233. 
"Solar salt," 192. 
Solder, 336. 
Solute, 4. 
Solution, 4, ^23- 

chemical, 5. 

colloidal, 155. 

definition of, 4. 

pressure, 44. 
. scope of word, 206. 

solid, 333. 
Solutions, general properties of, 44, 

molar, 70. 

normal, 70. 

saturated, 44. 

soHd, 322, 333. 

standard, 70. 

supersaturated, 45. 
Solvay soda process, 243. 
Solvent, 4. 
Soot, 88. 
Sorbite, 323. 
Spectroscope, 67. 
Speculum metal, 334. 



INDEX 



355 



" Spelter," 144. 

Sphalerite, 144, 234. 

Spinel, 239, 311. 

Spirits of hartshorn, 223. 

Stahl, G. E. (1660- 1 734), 78. 

Stalactites and stalagmites, 248. 

Stamping, 15 1. 

Stannic compounds, 140. 

oxide, 260. 

sulphide, 261. 
Stannous chloride, 200. 

compounds, 140. 

oxalate, 260. 

oxide, 260. 

sulphide, 261. 
Stannuni, 18, 138. 
Starch solution, 308. 
Stassfurt salts, 66, 67. 
Steel, 174. 

" cold short," 175. 

"red short," 175. 
Steels, alloy, 159, 336. 
Stibine, 189. 
Stibium, 18, 122. 
Stibnite, 122, 280. 
Stolzite, 160, 301. 
"Stoves," 172. 
Stromeyer, Friedrich ( 1 786-1835), 

148. 
Strontianite, 97, 127, 248. 
Strontium, 18, 127. 

carbonate, 248. 

nitrate, 272. 

oxide, 229, 231. 
Stucco, 292. 
Substitution, 55. 
Sulphates, 113, 290. 
Sulphydrates, 219. 
Sulphides, 113, 218. 

of the iron sub-group, 318. 
Sulphites, 283. 
" Sulphonating," 284. 
Sulphur, 18, 113. 

chlorides, 202. 



dioxide, 121, 282. 

flowers of, 113. 

hydrides, 185. 

insoluble, 115. 

milk of, 115. 

monoclinic, 115. . 

native, 113. 

octahedral, 115. 

oxides of, 282. 

plastic, 115. 

prismatic, 115. 

properties, 114. 

rhombic, 115. 

rolled, 113. 

trioxide, 283. 
" Sulphurets," 150. 
Sulphuretted hydrogen, 185. 
Supersaturation, 45. 
Syenite, 252. 
Sylvanite, 116, 150. 
Sylvite, 193. 
Symbols, 20. 

Sympathetic ink, 204, 318. 
Synthesis, 9. 

"Tailings," 152. 
Talc, 126. 
Tantalum, 18, 158. 

pentoxide, 281. 
Targioni, 87. 
Taylor, process of, 250. 
Telluretted hydrogen, 186. 
Tellurides, 219, 319. 
Tellurium, 18, 116. 

dioxide, 296. 

hydride, 186. 

trioxide, 297. 
Temperature, critical, 75. 
"Tempering," 174. 
Tennant, Smithson (1761-1815), 

182. 
Terbium, 18. 
Tetrachlormethane, 199. 
Tetragonal system, 46. 



356 



INDEX 



Thallium, i8, 134. 

chloride, 198. 

oxides, 239. 
Thenard, L, J, (1777-1857), 66, 183. 
Thenard's blue, 318. 
Theory, 1 1. • 

Thermit, 131. 
Thermometers, 147, 334. 
Thio-arsenates and -arsenites, 279. 
Thiocyanates, 328. 
Thiosulphates, 288. 

Thomson, J. J. (1856 ), 12. 

Thoria, 259. 
Thorite, 137. 
Thorium, 18, 137. 

carbide, 321. 

dioxide, 259. 

halides, 200. 
Thorpe, T. E., 165. 
Thulium, 18, 133. 
Thyroid gland, extract from, 55. 
Tin, 18, 138. 

alloys, 140. 

amalgams, 335. 

'•cry," 139^. 

" disease," 139. 

oxides, 260. 

plate, 140, 175. 

stone, 260. 

sulphides, 261. 

tetrachloride, 200. 
Tincal, 236. 
Titanium, 18, 137. 

dioxide, 259. 

tetrachloride, 200. 

trichloride, 200. 
Toning, 196. 
Transmutation, 16. 
Traube, Moritz (1826-1894), 207. 
Travers, M. W., 81. 
Tricalcic orthophosphate, 276. 
Triclinic system, 47. 
Tridymite, 252. 
Trimethylamine, 245. 



Troostite, 323. 
Trough, pneumatic, 23. 
Tungstates, 301. 
Tungsten, 18, 160. 

" bronze," 301. 

trioxide, 301. 
Turnhull's blue, 329. 
Tuyeres, 172. 
Type-element, ill. 

Unsaturated compounds, 103. 
Uraninite, 81, 160, 164, 301. 
Uranium, 18, 160. 

carbide, 321. 

oxides, 301. 
Uranyl nitrate, 301. 
Urea, 306, 327. 
Urine, 328. 

Valence, 102, 105. 

Valentine, Basil {circa 1400), 60, 

122, 123. 
Vanadium, 18, 157. 

oxides, 281. 
Vapor density, 194. ■ 

pressure, 49. 

tension, 49. 
"Varec," 242. 

Vauquelin, L. N. ( 1 763-1 829), 128, 
161. 

Venable, F. p. (1856 ), 107. 

Venetian red, 316. 
Vermilion, 234. 
Victorium, 133. 
" Vital force," 328. 
Vitriol, blue, 291. 

green, 294. 

oil of, 284. 

white, 292. 
Volta, Count ' Alessandro (1745- 
1827), 91. 

Ward, 284. 
Water, 34. 



INDEX 



357 



composition, 36. 

distilled, 34. 

electrolysis of, 27, 36. 

gas, 94, 95, 100. 

glass, 222, 253. 

hard, 39. 

mineral, 39. 

occurrence, 34. 

physical properties, 35. 

potability of, 40. 

practical considerations, 39. 

purification, 41. 

rain, 39. 

theoretical considerations, 44. 
Watt, James (1736-18 19), 26. 
Weights, atomic, 12, 18, 19, 106. 

molecular, 35, 205. 
Welshach mantle, 94, 259. 
White arsenic, 277. 

iron, 321. 

lead, 249, 294. 

vitriol, 292. 
Willemite, 144. 
Winkler, Clemens (1838-1904), 138, 

142. 
Witherite, 127, 248. 

WOHLER, FRIEDRICH (180O-1882), 

128, 130, 321, 328. 
Wolframite, 160, 301. 
Wolframium, 18, 161. 



WOLLASTON, W. H. (1 766- 1 828), 

182. 

WoUastonite, 256. 
Wood ashes, 66. 
" Wood's metal," 336. 
Wulfenite, 141, 160, 301. 

Xenon, 18, 81. 

Yellow ocher, 316. 
Ytterbium, 18. 
Yttrium, 18, 133, 135. 

Zinc, 18, 144. 

blende, 113, 144. 

carbonate, 248. 

chloride, 197. 

" dust," 145. 

hydroxide, 233. 

oxide, 232. 

red ore of, 232. 

sulphate, 292. 

sulphide, 234. 

white, 233. 
Zincite, 232. 
Zircon, 137. 
Zirconia, 259. 
Zirconium,_i8, 137. 

dioxide, 259. 

halides, 200. 



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leges. ^I.IO. 

Orndorff's Laboratory Manual in Organic Chemistry. Boards. 35 cents. 

Palmer's Questions and Problems in Chemistry. 20 cents. 

Pepoon, Mitchell and Maxwell's Plant Life. A laboratory guide. 50 cents. 

Remsen's Organic Chemistry. $1.20. 

Roberts's Stereo-Chemistry. Its development and present aspects. $1.00. 

Sanford's Experimental Psychology. Part I. Sensation and perception. ^1.50. 

Schoch's Experiments and Discussions in Chemistry. 50 cents. 

Shaler's First Book in Geology. Cloth, 60 cents. Boards, 45 cents. 

Shepard's Inorganic Chemistry. Descriptive and qualitative. $1.12. 

Shepard's Briefer Course in Chemistry, with chapter on Organic Chemistry. 80 cts. 

Shepard's Laboratory Note-Book. Boards. 35 cents. 

Spalding's Botany. Practical exercises in the study of plants. 80 cents. 

Stevens's Introduction to Botany. Illustrated. $1.25. Key and Flora, 40 cents. 

Botany, with Key and Flora, $1.50. 
Stevens's Chemistry Note-Book. Laboratory sheets and covers. 50 cents. 
Venable's Short History of Chemistry. For students and the general reader. $1.00. 
Weed and Crossman's Laboratory Guide in Zoology. Emphasises essentials. 60 cts 
Whiting's Physical Measurement. Parts I -IV, in one volume. ^3.75. 
Whiting's Mathematical and Physical Tables. Paper. 50 cents. 

For eletnefitary ivorks see ozir list of books in Elementary Scie?ice. 

^. C. HEATH & CO.. Publishers, Boston, New York, Chicago 



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